correcting a comparison

git-svn-id: https://svn.ssec.wisc.edu/repos/glance/trunk@66 8a9318a1-56ba-4d59-b755-99d26321be01

pyglance/glance/delta.py

@@ -128,7 +128,7 @@ def stats(diffData, mask, *etc):
     # if there are no values after the mask,
     # we can't do any of these forms of
     # statistical analysis
-    if sum(mask) is 0 :
+    if sum(mask) <= 0 :
         return { }
     
     absDiffData = abs(diffData)