gtkdoc-check: Don’t raise an exception if Makefile doesn’t exist
If running gtkdoc-check on a project built by Meson, neither Makefile.am or Makefile will exist. We can set the gtkdoc-check configuration via environment variables, which is fine; except that the get_variable() code raises an exception if the variable is not found in the Makefile. If the Makefile is missing, lines == [], which would cause the exception to be raised.
Fix this by only grepping for the variable in the Makefile if it’s not set in the environment.
Signed-off-by: Philip Withnall withnall@endlessm.com
This also includes a small, unrelated typo fix.