font-patcher: Limit vertical overlap

[why]
The vertical overlap has never been a problem (as far as I know). It is
maybe good to have some overlap for the terminal emulators that support
vertical overlap.
On terminals that truncate at the nominal cell border too much overlap
looks bad, i.e. the glyphs 'distorted'.

If we ever increase the overlap it is most likely be meant to be the
left-right overlap.

[note]
Originally this has been part of commit fecda6a of #780.

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

font-patcher

@@ -1038,7 +1038,7 @@ class font_patcher:
             if scale_ratio_x != 1 or scale_ratio_y != 1:
                 if overlap:
                     scale_ratio_x *= 1 + overlap
-                    scale_ratio_y *= 1 + overlap
+                    scale_ratio_y *= 1 + max(0.01, overlap) # never aggressive vertical overlap
                 self.sourceFont[currentSourceFontGlyph].transform(psMat.scale(scale_ratio_x, scale_ratio_y))
 
             # Use the dimensions from the newly pasted and stretched glyph