Fix: File output uses incorrect resolution when first socket unused.

File output node always received the resolution from the first socket.
When that socket didn't had a link it would use a resolution of 0,0.
What lead to not saving the file at all.

This only effected Multi layer OpenEXR files.
This change would go over all the links to find the first valid
resolution.

source/blender/compositor/operations/COM_OutputFileOperation.cc

@@ -323,6 +323,7 @@ OutputOpenExrMultiLayerOperation::OutputOpenExrMultiLayerOperation(const Scene *
   this->m_exr_codec = exr_codec;
   this->m_exr_half_float = exr_half_float;
   this->m_viewName = viewName;
+  this->setResolutionInputSocketIndex(RESOLUTION_INPUT_ANY);
 }
 
 void OutputOpenExrMultiLayerOperation::add_layer(const char *name,