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.

[note2]
Originally this has been part of PR #967.
Although that had a bug 😬
It used max() instead of min() (T_T)

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

font-patcher

@@ -676,6 +676,7 @@ class font_patcher:
     def setup_patch_set(self):
         """ Creates list of dicts to with instructions on copying glyphs from each symbol font into self.sourceFont """
         # Supported params: overlap | careful
+        # Overlap value is used horizontally but vertically limited to 0.01
         # Powerline dividers
         SYM_ATTR_POWERLINE = {
             'default': {'align': 'c', 'valign': 'c', 'stretch': 'pa', 'params': {}},
@@ -1118,6 +1119,7 @@ class font_patcher:
             overlap = sym_attr['params'].get('overlap')
             if overlap:
                 scale_ratio_x *= 1.0 + (self.font_dim['width'] / (sym_dim['width'] * scale_ratio_x)) * overlap
+                overlap = min(0.01, overlap) # never aggressive vertical overlap
                 scale_ratio_y *= 1.0 + (self.font_dim['width'] / (sym_dim['width'] * scale_ratio_y)) * overlap
 
             # Size in x to size in y ratio limit (to prevent over-wide glyphs)