pyplot: check for existence of cnt.collections before access

(probably some newer matplotlib is different, visual
impression seemingly not affected)

Author: j-fu

src/pyplot.jl

@@ -600,10 +600,12 @@ function scalarplot!(ctx, TP::Type{PyPlotType}, ::Type{Val{2}}, grids, parentgri
         cmap = PyPlot.ColorMap(plaincolormap(ctx)),
     )
 
-    for c in cnt.collections
-        c.set_edgecolor("face")
+    if hasproperty(cnt,:collections)
+        for c in cnt.collections
+            c.set_edgecolor("face")
+        end
     end
-
+    
     ax.tricontour(tdat..., func; colors = "k", levels = levels)
 
     if ctx[:colorbar] == :horizontal