Macros from temporary diff blueprints can be placed and corrupt blueprint

Following the repro, a temporary copy of a BP Macro library is loaded into memory. When you right click to place a node, it incorrectly lists macros defined in this temporary library. They are fully placeable and it will save. However if you transfer this to another machine or delete your temp folder, that macro will break as it is pointing to an invalid library.

In my testing diffing BP Function libraries and individual BPs did not expose the temp functions, so it might be a macro-specific issue.

1. Load into a game (like QAGame) that is hooked up to p4 source control
2. Load the engine StandardMacros macro library
3. Right click and duplicate the CompareFloat macro, do not save
4. Click the File menu, then diff, then depot. This will load a temporary version of the StandardMacros library into memory
5. Go to any blueprint, right click, and type CompareFloat. You will get two copies of compare float (as well as your duplicated comparefloat_0). One of them is actually the macro from the temporary blueprint and will corrupt on save