[client] ds: validate the ds before attempting to use it

client/include/interface/displayserver.h

@@ -141,4 +141,26 @@ struct LG_DisplayServerOps
   void (*cbRequest)(LG_ClipboardData type);
 };
 
+#define IS_LG_DS_VALID(x) \
+  ((x)->probe              && \
+   (x)->earlyInit          && \
+   (x)->init               && \
+   (x)->startup            && \
+   (x)->shutdown           && \
+   (x)->free               && \
+   (x)->getProp            && \
+   (x)->getEGLDisplay      && \
+   (x)->getEGLNativeWindow && \
+   (x)->glSwapBuffers      && \
+   (x)->showPointer        && \
+   (x)->grabPointer        && \
+   (x)->ungrabPointer      && \
+   (x)->warpPointer        && \
+   (x)->realignPointer     && \
+   (x)->isValidPointerPos  && \
+   (x)->inhibitIdle        && \
+   (x)->uninhibitIdle      && \
+   (x)->wait               && \
+   (x)->setWindowSize      && \
+   (x)->setFullscreen)
 #endif

client/src/main.c

@@ -633,6 +633,7 @@ static int lg_run(void)
     }
 
   assert(g_state.ds);
+  assert(IS_LG_DS_VALID(g_state.ds));
 
   // init the subsystem
   if (!g_state.ds->earlyInit())