Fixed shebangs, added error checking

samples/python2/distrans.py

@@ -1,4 +1,4 @@
-#/usr/bin/env python
+#!/usr/bin/env python
 
 '''
 Distance transform sample.
@@ -15,15 +15,22 @@ Keys:
 import numpy as np
 import cv2
 import cv2.cv as cv
+
 from common import make_cmap
 
 if __name__ == '__main__':
     import sys
-    try: fn = sys.argv[1]
-    except: fn = '../cpp/fruits.jpg'
+    try:
+        fn = sys.argv[1]
+    except:
+        fn = '../cpp/fruits.jpg'
     print __doc__
 
     img = cv2.imread(fn, 0)
+    if img is None:
+        print 'Failed to load fn:', fn
+        sys.exit(1)
+        
     cm = make_cmap('jet')
     need_update = True
     voronoi = False