Don't crash on malformed HTML in wxHTML font tag handler.

Don't try to access the first character of the size parameter value before we
are sure that it is not empty.

Closes #12812.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66492 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/html/m_fonts.cpp

@@ -51,10 +51,11 @@ TAG_HANDLER_BEGIN(FONT, "FONT" )
 
         if (tag.HasParam(wxT("SIZE")))
         {
-            int tmp = 0;
-            wxChar c = tag.GetParam(wxT("SIZE")).GetChar(0);
-            if (tag.GetParamAsInt(wxT("SIZE"), &tmp))
+            long tmp = 0;
+            const wxString sizeStr = tag.GetParam(wxT("SIZE"));
+            if (sizeStr.ToLong(&tmp))
             {
+                wxChar c = sizeStr[0];
                 if (c == wxT('+') || c == wxT('-'))
                     m_WParser->SetFontSize(oldsize+tmp);
                 else