Correctly recognize when wglChoosePixelFormatARB() fails.

This function returns TRUE even if it failed to find any matching formats, so
test not only its return value but also the number of formats it found.

Closes #12474.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65575 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/glcanvas.cpp

@@ -493,12 +493,21 @@ static int ChoosePixelFormatARB(HDC hdc, const int *attribList)
 
     int pf;
     UINT numFormats = 0;
+
     if ( !wglChoosePixelFormatARB(hdc, iAttributes, NULL, 1, &pf, &numFormats) )
     {
         wxLogLastError(wxT("wglChoosePixelFormatARB"));
         return 0;
     }
 
+    // Although TRUE is returned if no matching formats are found (see
+    // http://www.opengl.org/registry/specs/ARB/wgl_pixel_format.txt), pf is
+    // not initialized in this case so we need to check for numFormats being
+    // not 0 explicitly (however this is not an error so don't call
+    // wxLogLastError() here).
+    if ( !numFormats )
+        pf = 0;
+
     return pf;
 }