More warnings fixed.

Rev: src/modules/Image/encodings/bmp.c:1.25
Rev: src/modules/Image/encodings/gif.c:1.54
Rev: src/modules/Image/encodings/png.c:1.35
Rev: src/modules/Image/encodings/x.c:1.29
Rev: src/modules/Image/encodings/xwd.c:1.16