Fix GpuConv error reporting. The error was raised in the next executed apply…

theano/sandbox/cuda/blas.py

@@ -652,7 +652,7 @@ class GpuConv(GpuOp):
 
     def c_code_cache_version(self):
         # raise this whenever modifying any of the support_code_files
-        return (0, 19)
+        return (0, 20)
 
     def c_support_code_apply(self, node, nodename):
         # REMEMBER TO RAISE c_code_cache_version when changing any of
@@ -711,6 +711,10 @@ class GpuConv(GpuOp):
                                                          %(max_threads_dim0)s);
     Py_XDECREF(%(out)s);
     %(out)s = out2;
+
+    if (%(out)s==NULL){
+        %(fail)s
+    }
 """ % sub