CAM: Adjusted Fanuc post processing script to always start with a percent

The percent signal to the machine that a program follows, and is not
part of the header but a required part when uploading programs into
the machine.

src/Mod/CAM/Path/Post/scripts/fanuc_post.py

@@ -230,9 +230,10 @@ def export(objectslist, filename, argstring):
     print("postprocessing...")
     gcode = ""
 
+    gcode += "%\n"
+
     # write header
     if OUTPUT_HEADER:
-        gcode += "%\n"
         gcode += ";\n"
         gcode += (
             os.path.split(filename)[-1]