Internals: Breaking: ImRect() default constructor initializes all fields with 0.0f

Instead of (FLT_MAX,FLT_MAX,-FLT_MAX,-FLT_MAX). Previous behavior was designed for adding into a bounding box but rarely relied on and not worth it.

imgui_internal.h

@@ -644,7 +644,7 @@ struct IMGUI_API ImRect
     ImVec2      Min;    // Upper-left
     ImVec2      Max;    // Lower-right
 
-    ImRect()                                        : Min(FLT_MAX,FLT_MAX), Max(-FLT_MAX,-FLT_MAX)  {}
+    ImRect()                                        : Min(0.0f, 0.0f), Max(0.0f, 0.0f)              {}
     ImRect(const ImVec2& min, const ImVec2& max)    : Min(min), Max(max)                            {}
     ImRect(const ImVec4& v)                         : Min(v.x, v.y), Max(v.z, v.w)                  {}
     ImRect(float x1, float y1, float x2, float y2)  : Min(x1, y1), Max(x2, y2)                      {}