Bug fix icon.c crashes with negative icon index

The index for Icon_NOICON is -1 which is caught properly
as is icon > Icon_Last_Themeable

But if you pass an index lower than Icon_NOICON screen_put_iconxy()
tries to read memory prior to the iconset resulting in a crash

Change-Id: I415e650932d65214d883a1595e22261f22e776b6
2 files changed