Backends: WebGPU: include imgui.h before backend check (#8437)

backends/imgui_impl_wgpu.cpp

@@ -41,6 +41,8 @@
 //  2021-02-18: Change blending equation to preserve alpha in output buffer.
 //  2021-01-28: Initial version.
 
+#include "imgui.h"
+
 // When targeting native platforms (i.e. NOT emscripten), one of IMGUI_IMPL_WEBGPU_BACKEND_DAWN
 // or IMGUI_IMPL_WEBGPU_BACKEND_WGPU must be provided. See imgui_impl_wgpu.h for more details.
 #ifndef __EMSCRIPTEN__
@@ -53,7 +55,6 @@
     #endif
 #endif
 
-#include "imgui.h"
 #ifndef IMGUI_DISABLE
 #include "imgui_impl_wgpu.h"
 #include <limits.h>