AutoTest: Fix reparsing of header files...

...when having split source and headers and defining test data functions
inside the source file.
If we just reparse a header file (e.g. when opening the respective file
inside the editor) we have no explicit information where the definition
of the functions is. This lead to not finding the information necessary
for displaying data tags and throwing away old information as they have
been marked for removal.

Change-Id: Ieb8ed9f7c758fe2c793e60ca2c30b4025106363b
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>