Fix search button height in generic wxSearchCtrl

Make this button of exactly the bitmap size instead of using the full
control height for it, even if/when the bitmap is smaller.

This fixes some random junk being shown in the bottom two pixels of the
search button sometimes: this was due to only redrawing the part covered
by the bitmap in wxSearchButton::OnPaint(), leaving the rest of the
button unpainted (because wxSearchButton uses wxBG_STYLE_PAINT).

src/generic/srchctlg.cpp

@@ -504,7 +504,7 @@ void wxSearchCtrl::LayoutControls()
     // position the subcontrols inside the client area
 
     m_searchButton->SetSize(x, (height - sizeSearch.y) / 2,
-                            sizeSearch.x, height);
+                            sizeSearch.x, sizeSearch.y);
     x += sizeSearch.x;
     x += searchMargin;