hal_glib.py: prevent emitting 'file-loaded' if file_new is empty.

Fixes an edge case where 'file-loaded' would be emitted even if file_new was empty.  This was inadvertantly caused by commit 40e4a23.  The edge case surrounds calling a subroutine from file via MDI before any other file was loaded.

Author: snowgoer540

lib/python/hal_glib.py

@@ -491,7 +491,7 @@ def update(self):
             # file name if call level != 0 in the merge() function above.
             # do avoid that a signal is emitted in that case, causing
             # a reload of the preview and sourceview widgets
-            if self.stat.interp_state == linuxcnc.INTERP_IDLE:
+            if self.stat.interp_state == linuxcnc.INTERP_IDLE and file_new != "":
                 self.emit('file-loaded', file_new)
 
         #ToDo : Find a way to avoid signal when the line changed due to