shapes.c: Initialize `pointf p` variable.
shapes.c: Initialize `pointf p` variable.

Because this variable was used uninitialized, it caused a runtime error on
Windows.

ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz,ellson/graphviz