Catch exception if shape file does not include a thumbnail.

src/Mod/Path/PathScripts/PathToolBit.py

@@ -322,11 +322,14 @@ class ToolBit(object):
             path = findShape(obj.BitShape)
             if path:
                 with open(path, 'rb') as fd:
-                    zf = zipfile.ZipFile(fd)
-                    pf = zf.open('thumbnails/Thumbnail.png', 'r')
-                    data = pf.read()
-                    pf.close()
-                    return data
+                    try:
+                        zf = zipfile.ZipFile(fd)
+                        pf = zf.open('thumbnails/Thumbnail.png', 'r')
+                        data = pf.read()
+                        pf.close()
+                        return data
+                    except KeyError:
+                        pass
         return None
 
     def saveToFile(self, obj, path, setFile=True):