[ui] Camera Response Function display: make it safer

More checks on file content and catch exception.
Check nbColumns using a slot instead of using the property.
Use a workaround on the CVS loader to avoid a crash (do not set active
to False).

meshroom/core/node.py

@@ -499,6 +499,7 @@ class BaseNode(BaseObject):
     def getAttributes(self):
         return self._attributes
 
+    @Slot(str, result=bool)
     def hasAttribute(self, name):
         return name in self._attributes.keys()