only touch .zlib if it's not already there

compile.sh

@@ -207,7 +207,7 @@ export VLC_EXTRA_CFLAGS="${EXTRA_CFLAGS}"
 
 make fetch
 # We already have zlib available
-mkdir -p zlib; touch .zlib
+[ -e .zlib ] || (mkdir -p zlib; touch .zlib)
 make $MAKEFLAGS
 
 cd ../.. && mkdir -p android && cd android