Cleared m_scriptFilename between scene files. (#2278)

This fixes a bug where a Python script file would be run on a scene file
that didn't have a script file set.
Added a general case version to SceneBuilderWorker.cpp, to make it easy
to mark all scene files as dirty.
Automated tests for this will come in a separate pull request.

Signed-off-by: stankowi <4838196+AMZN-stankowi@users.noreply.github.com>

Gems/SceneProcessing/Code/Source/SceneBuilder/SceneBuilderWorker.cpp

@@ -74,6 +74,8 @@ namespace SceneBuilder
             {
                 m_cachedFingerprint.append(element);
             }
+            // A general catch all version fingerprint. Update this to force all FBX files to recompile.
+            m_cachedFingerprint.append("Version 1");
         }
 
         return m_cachedFingerprint.c_str();