ImDrawList: fixed index overflow check broken by AddText(). Added extra assert. (#514)

imgui.cpp

@@ -2289,7 +2289,8 @@ static void AddDrawListToRenderList(ImVector<ImDrawList*>& out_render_list, ImDr
         // If this assert triggers because you are drawing lots of stuff manually, A) workaround by calling BeginChild()/EndChild() to put your draw commands in multiple draw lists, B) #define ImDrawIdx to a 'unsigned int' in imconfig.h and render accordingly.
         const unsigned long long int max_vtx_idx = (unsigned long long int)1L << (sizeof(ImDrawIdx)*8);
         (void)max_vtx_idx;
-        IM_ASSERT((unsigned long long int)draw_list->_VtxCurrentIdx <= max_vtx_idx); // Too many vertices in same ImDrawList
+        IM_ASSERT((int)draw_list->_VtxCurrentIdx == draw_list->VtxBuffer.Size);         // Sanity check. Bug or mismatch between PrimReserve() calls and incrementing _VtxCurrentIdx, _VtxWritePtr etc.
+        IM_ASSERT((unsigned long long int)draw_list->_VtxCurrentIdx <= max_vtx_idx);    // Too many vertices in same ImDrawList. See comment above.
 
         GImGui->IO.MetricsRenderVertices += draw_list->VtxBuffer.Size;
         GImGui->IO.MetricsRenderIndices += draw_list->IdxBuffer.Size;

imgui_draw.cpp

@@ -903,7 +903,7 @@ void ImDrawList::AddText(const ImFont* font, float font_size, const ImVec2& pos,
     CmdBuffer.back().ElemCount -= idx_unused;
     _VtxWritePtr -= vtx_unused;
     _IdxWritePtr -= idx_unused;
-    _VtxCurrentIdx = (ImDrawIdx)VtxBuffer.Size;
+    _VtxCurrentIdx = (unsigned int)VtxBuffer.Size;
 }
 
 // This is one of the few function breaking the encapsulation of ImDrawLst, but it is just so useful.