Avoid compilation warning in frame.c

* src/frame.c (Fx_parse_geometry): Avoid compilation warning
about x and y being used without initializing them.
1 job for master in 3 minutes and 27 seconds (queued for 1 second)
Status Job ID Name Coverage
failed #3107


Name Stage Failure
test-all Test
Makefile:402: recipe for target 'xdisp.o' failed
make[2]: Leaving directory '/builds/emacs/emacs/src'
make[2]: *** [xdisp.o] Error 1
Makefile:424: recipe for target 'src' failed
make[1]: Leaving directory '/builds/emacs/emacs'
Makefile:1117: recipe for target 'bootstrap' failed
make[1]: *** [src] Error 2
make: *** [bootstrap] Error 2
ERROR: Job failed: exit code 1