Don't unnecessarily drop LTR kerns when combining with RTL

[anthrotype]

Fixes #1039

--- master_ufo/PlaypenSans-Regular.ufo/kerning.plist	2024-10-31 10:32:42
+++ master_ufo_2/PlaypenSans-Regular.ufo/kerning.plist	2024-10-31 10:32:52
@@ -14,7 +14,11 @@
     </dict>
     <key>public.kern1.quotesingle</key>
     <dict>
+      <key>public.kern2.A</key>
+      <integer>-49</integer>
       <key>public.kern2.bet-hb</key>
+      <integer>-20</integer>
+      <key>public.kern2.space</key>
       <integer>-20</integer>
     </dict>
     <key>public.kern1.space</key>

[anthrotype]

maybe I'll try to distill a unit test from Simon's test file

EDIT: did that in #1042

[simoncozens]

LGTM, thank you!