Blender Git Loki

Fix: Large stack allocation in compositor

When COM_EXPORT_GRAPHVIZ is enabled, DebugInfo::graphviz
uses a char[1000000] as local variable. When this function
is called this is allocated on the stack, which has a size
of just 1MB on mac and may cause a stack overflow.

This patch allocates the memory on the heap and frees
the memory at the end of the function.

Reviewed By: LazyDodo

Differential Revision: https://developer.blender.org/D13628