BF: If DTIFitTensor image objects don't have a nvals property

fsleyes/gl/gllinevector.py

@@ -80,7 +80,7 @@ class GLLineVector(glvector.GLVector):
                 # Vector images stored as RGB24 data
                 # type are assumed to map from [0, 255]
                 # to [-1, 1], so cannot be normalised
-                if image.nvals > 1:
+                if vecImage.nvals > 1:
                     return data
 
                 # calculate lengths

fsleyes/gl/glrgbvector.py

@@ -86,7 +86,7 @@ class GLRGBVector(glvector.GLVector):
             # Vector images stored as RGB24 data
             # type are assumed to map from [0, 255]
             # to [-1, 1], so cannot be normalised
-            if image.nvals > 1:
+            if vecImage.nvals > 1:
                 return data
 
             # make absolute, and scale to unit