SDL, SDL2: SDL{,2}_PATH may be undefined

pkgs/development/libraries/SDL/setup-hook.sh

@@ -1,6 +1,6 @@
 addSDLPath () {
   if [ -e "$1/include/SDL" ]; then
-    export SDL_PATH="$SDL_PATH $1/include/SDL"
+    export SDL_PATH="${SDL_PATH-}${SDL_PATH:+ }$1/include/SDL"
   fi
 }
 

pkgs/development/libraries/SDL2/setup-hook.sh

@@ -1,6 +1,6 @@
 addSDL2Path () {
   if [ -e "$1/include/SDL2" ]; then
-    export SDL2_PATH="$SDL2_PATH $1/include/SDL2"
+    export SDL2_PATH="${SDL2_PATH-}${SDL2_PATH:+ }$1/include/SDL2"
   fi
 }