shader_glsl.c: Move buffer null pointer check in gl_glsl_set_coords()

`buffer` is initialized to a statically allocated variable and can only be NULL
when the allocation of a bigger buffer fails. When only the core frame is being
displayed, the buffer never points to the heap thanks to the small buffer
optimization.

gfx/drivers_shader/shader_glsl.c

@@ -1443,10 +1443,10 @@ static bool gl_glsl_set_coords(void *shader_data,
       elems        *= coords->vertices * sizeof(GLfloat);
 
       buffer        = (GLfloat*)malloc(elems);
-   }
 
-   if (!buffer)
-      return false;
+      if (!buffer)
+         return false;
+   }
 
    if (uni->tex_coord >= 0)
    {