Fixed bug 4544 - SDL2.m4 SDL2.framework patch made it impossible to fail detection

Stian Skjelstad

check if $sdl_framework is set, before checking if directory exists

Patch that was merged here https://hg.libsdl.org/SDL/rev/9befd0acb9ef made it impossible for the SDL2 detection to fail, since one of the if statements fails to check if a variable is set or not.

if test -d $sdl_framework; then

can evaluate to true in some shells. I guess it falls into undefined behaviour when looking at the POSIX standard.

sdl2.m4

@@ -74,7 +74,7 @@ AC_ARG_VAR(SDL2_FRAMEWORK, [Path to SDL2.framework])
         done
       fi
 
-      if test -d $sdl_framework; then
+      if test x"$sdl_framework" != x && test -d "$sdl_framework"; then
         AC_MSG_RESULT($sdl_framework)
         sdl_framework_dir=`dirname $sdl_framework`
         SDL_CFLAGS="-F$sdl_framework_dir -Wl,-framework,SDL2 -I$sdl_framework/include"