Don't create an empty 'stella.pro' file when possible.

- Not a big deal, but several people are complaining when 'ghost' files are created
- If file doesn't already exist and there is nothing to add, simply don't create one
- Alternatively, we should delete the file if it's zero-sized, but that requires changes to FSNode.

src/emucore/OSystem.cxx

@@ -203,11 +203,8 @@ void OSystem::saveConfig()
   logMessage("Saving config options ...", 2);
   mySettings->save(configFile());
 
-  if(myPropSet)
+  if(myPropSet && myPropSet->save(myPropertiesFile))
-  {
     logMessage("Saving properties set ...", 2);
-    myPropSet->save(myPropertiesFile);
-  }
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

src/emucore/PropsSet.cxx

@@ -42,6 +42,11 @@ void PropertiesSet::load(const string& filename)
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 bool PropertiesSet::save(const string& filename) const
 {
+  // Only save properties when it won't create an empty file
+  FilesystemNode props(filename);
+  if(!props.exists() && myExternalProps.size() == 0)
+    return false;
+
   ofstream out(filename);
   if(!out)
     return false;

src/emucore/PropsSet.hxx

@@ -58,8 +58,10 @@ class PropertiesSet
 
       @param filename  Full pathname of output file to use
 
-      @return  True on success, false on failure
+      @return  True on success, false on failure or save not needed
-               Failure occurs if file couldn't be opened for writing
+               Failure occurs if file couldn't be opened for writing,
+               or if the file doesn't exist and a zero-byte file
+               would be created
     */
     bool save(const string& filename) const;