don't abort fgfs only because a nasal script called a property function

with an invalid path, as in getprop("/sim/model/737") or x.getNode("f:1").
Forward sg's error message to the Nasal runtime error function instead, so
you get something like:

  Nasal runtime error: name must begin with alpha or '_'
    at /home/m/fgfs/Base.local/Nasal/props.nas, line 30

Unfortunately, the location points to the line where the ghost wrapper
sits, rather than the offending script line.

src/Scripting/NasalSys.cxx

@@ -124,12 +124,17 @@ void FGNasalSys::hashset(naRef hash, const char* key, naRef val)
 static SGPropertyNode* findnode(naContext c, naRef* vec, int len)
 {
     SGPropertyNode* p = globals->get_props();
+    try {
         for(int i=0; i<len; i++) {
             naRef a = vec[i];
             if(!naIsString(a)) return 0;
             p = p->getNode(naStr_data(a));
             if(p == 0) return 0;
         }
+    } catch (const string& err) {
+        naRuntimeError(c, (char *)err.c_str());
+        return 0;
+    }
     return p;
 }
 
@@ -185,8 +190,12 @@ static naRef f_setprop(naContext c, naRef me, int argc, naRef* args)
 
     SGPropertyNode* props = globals->get_props();
     naRef val = args[argc-1];
+    try {
         if(naIsString(val)) props->setStringValue(buf, naStr_data(val));
         else                props->setDoubleValue(buf, naNumValue(val).num);
+    } catch (const string& err) {
+        naRuntimeError(c, (char *)err.c_str());
+    }
     return naNil();
 #undef BUFLEN
 }

src/Scripting/nasal-props.cxx

@@ -157,11 +157,16 @@ static naRef f_getChild(naContext c, naRef me, int argc, naRef* args)
     naRef idx = naNumValue(naVec_get(argv, 1));
     bool create = naTrue(naVec_get(argv, 2));
     SGPropertyNode* n;
+    try {
         if(naIsNil(idx) || !naIsNum(idx)) {
             n = (*node)->getChild(naStr_data(child), create);
         } else {
             n = (*node)->getChild(naStr_data(child), (int)idx.num, create);
         }
+    } catch (const string& err) {
+        naRuntimeError(c, (char *)err.c_str());
+        return naNil();
+    }
     if(!n) return naNil();
     return propNodeGhostCreate(c, n);
 }
@@ -178,10 +183,15 @@ static naRef f_getChildren(naContext c, naRef me, int argc, naRef* args)
         // Get all children of a specified name
         naRef name = naVec_get(argv, 0);
         if(!naIsString(name)) return naNil();
+        try {
             vector<SGPropertyNode_ptr> children
                 = (*node)->getChildren(naStr_data(name));
             for(unsigned int i=0; i<children.size(); i++)
                 naVec_append(result, propNodeGhostCreate(c, children[i]));
+        } catch (const string& err) {
+            naRuntimeError(c, (char *)err.c_str());
+            return naNil();
+        }
     }
     return result;
 }
@@ -192,7 +202,11 @@ static naRef f_removeChild(naContext c, naRef me, int argc, naRef* args)
     naRef child = naVec_get(argv, 0);
     naRef index = naVec_get(argv, 1);
     if(!naIsString(child) || !naIsNum(index)) return naNil();
+    try {
         (*node)->removeChild(naStr_data(child), (int)index.num, false);
+    } catch (const string& err) {
+        naRuntimeError(c, (char *)err.c_str());
+    }
     return naNil();
 }
 
@@ -208,10 +222,15 @@ static naRef f_removeChildren(naContext c, naRef me, int argc, naRef* args)
         // Remove all children of a specified name
         naRef name = naVec_get(argv, 0);
         if(!naIsString(name)) return naNil();
+        try {
             vector<SGPropertyNode_ptr> children
                 = (*node)->removeChildren(naStr_data(name), false);
             for(unsigned int i=0; i<children.size(); i++)
                 naVec_append(result, propNodeGhostCreate(c, children[i]));
+        } catch (const string& err) {
+            naRuntimeError(c, (char *)err.c_str());
+            return naNil();
+        }
     }
     return result;
 }
@@ -222,7 +241,13 @@ static naRef f_getNode(naContext c, naRef me, int argc, naRef* args)
     naRef path = naVec_get(argv, 0);
     bool create = naTrue(naVec_get(argv, 1));
     if(!naIsString(path)) return naNil();
-    SGPropertyNode* n = (*node)->getNode(naStr_data(path), create);
+    SGPropertyNode* n;
+    try {
+        n = (*node)->getNode(naStr_data(path), create);
+    } catch (const string& err) {
+        naRuntimeError(c, (char *)err.c_str());
+        return naNil();
+    }
     return propNodeGhostCreate(c, n);
 }