Remove redundant ShouldForwardFromEditToCombo() check

No real changes, just avoid calling ShouldForwardFromEditToCombo() in
MSWProcessEditMsg() because this function is only called when the
message should be forwarded.

Also make the comment about the return value more clear.

src/msw/combobox.cpp

@@ -277,15 +277,10 @@ bool wxComboBox::MSWProcessEditMsg(WXUINT msg, WXWPARAM wParam, WXLPARAM lParam)
             break;
     }
 
-    if ( ShouldForwardFromEditToCombo(msg) )
-    {
-        // For all the messages forward from the edit control the
-        // result is not used.
-        WXLRESULT result;
-        return MSWHandleMessage(&result, msg, wParam, lParam);
-    }
-
-    return false;
+    // For all the messages forwarded from the edit control the result is not
+    // used and 0 must be returned if the message is handled.
+    WXLRESULT result;
+    return MSWHandleMessage(&result, msg, wParam, lParam);
 }
 
 bool wxComboBox::MSWCommand(WXUINT param, WXWORD id)