APPEND_OUTER should evaluate variables in filename argument when IF_EXISTS is specified

[Argent77]

The following code snippet does not append text to the specified file %MOD_FOLDER%/test.txt.

<<<<<<<< .../inlined/test.txt
Original text
>>>>>>>>
COPY ~.../inlined/test.txt~ ~%MOD_FOLDER%/test.txt~
APPEND_OUTER ~%MOD_FOLDER%/test.txt~ ~Appended text~ IF_EXISTS

Produced log message:

Not appending to [%MOD_FOLDER%/test.txt] because the file does not exist

[FredrikLindgren]

Thanks. Fixed.