Fixed GCC warning.

3rdparty/ocornut-imgui/imgui.cpp

@@ -355,6 +355,7 @@
 #pragma GCC diagnostic ignored "-Wunused-function"          // warning: 'xxxx' defined but not used
 #pragma GCC diagnostic ignored "-Wunused-parameter"         // warning: unused parameter ‘xxxx’
 #pragma GCC diagnostic ignored "-Wtype-limits"              // warning: comparison is always true due to limited range of data type
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"      // warning: ‘xxxx’ may be used uninitialized in this function
 #endif
 
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