Remove bimg_encode from non-tools build.

scripts/genie.lua

@@ -371,7 +371,10 @@ bgfxProject("", "StaticLib", {})
 dofile(path.join(BX_DIR,   "scripts/bx.lua"))
 dofile(path.join(BIMG_DIR, "scripts/bimg.lua"))
 dofile(path.join(BIMG_DIR, "scripts/bimg_decode.lua"))
-dofile(path.join(BIMG_DIR, "scripts/bimg_encode.lua"))
+
+if _OPTIONS["with-tools"] then
+	dofile(path.join(BIMG_DIR, "scripts/bimg_encode.lua"))
+end
 
 if _OPTIONS["with-examples"] or _OPTIONS["with-tools"] then
 	group "examples"