[core] Exclude edges from InputNode nodes in dfsToProcess

If the edges of a node to submit include an `InputNode` (which cannot
be computed), then that node should be excluded from the list of edges
to process as if that node had already been computed.

This allows to submit any type of graph involving `InputNode` to the farm.

meshroom/core/node.py

@@ -811,6 +811,8 @@ class BaseNode(BaseObject):
         return True
 
     def _isComputed(self):
+        if not self.isComputable:
+            return True
         return self.hasStatus(Status.SUCCESS)
 
     def _isComputable(self):