Fix -Wconversion warning (#2379)
The warning was caused by implicit conversion from pointer type which
NULL has to non-pointer type, e.g. if ImTextureID is long int
diff --git a/imgui_draw.cpp b/imgui_draw.cpp
index 37e8ff5..25ce75f 100644
--- a/imgui_draw.cpp
+++ b/imgui_draw.cpp
@@ -407,7 +407,7 @@
// Using macros because C++ is a terrible language, we want guaranteed inline, no code in header, and no overhead in Debug builds
#define GetCurrentClipRect() (_ClipRectStack.Size ? _ClipRectStack.Data[_ClipRectStack.Size-1] : _Data->ClipRectFullscreen)
-#define GetCurrentTextureId() (_TextureIdStack.Size ? _TextureIdStack.Data[_TextureIdStack.Size-1] : NULL)
+#define GetCurrentTextureId() (_TextureIdStack.Size ? _TextureIdStack.Data[_TextureIdStack.Size-1] : (ImTextureID)NULL)
void ImDrawList::AddDrawCmd()
{
