Checked for uniqueness of the label

Author: pthpth

src/graphs.jl

@@ -51,9 +51,9 @@ Add a vertex to MetaGraph `g` with label `label` having value `val`.
 Return true if the vertex has been added, false incase the label already exists or edge was not added.
 """
 function add_vertex!(g::MetaGraph, label, val)
-    added = add_vertex!(g.graph)
     if g.haskey(label)
         return false
+    added = add_vertex!(g.graph)
     if added
         v = nv(g)
         g.vprops[label] = (v, val)