fix(highlight): apply fallback even if not defined

Fixes: #729

lua/gitsigns/highlight.lua

@@ -185,9 +185,17 @@ local function derive(hl, hldef)
          else
             vim.api.nvim_set_hl(0, hl, { default = true, link = d })
          end
-         break
+         return
       end
    end
+   if hldef[1] and not hldef.bg_factor and not hldef.fg_factor then
+
+
+      dprintf('Deriving %s from %s', hl, hldef[1])
+      vim.api.nvim_set_hl(0, hl, { default = true, link = hldef[1] })
+   else
+      dprintf('Could not derive %s', hl)
+   end
 end
 
 

teal/gitsigns/highlight.tl

@@ -185,9 +185,17 @@ local function derive(hl: string, hldef: Hldef)
       else
         vim.api.nvim_set_hl(0, hl, {default = true, link = d })
       end
-      break
+      return
     end
   end
+  if hldef[1] and not hldef.bg_factor and not hldef.fg_factor then
+    -- No fallback found which is set. Just link to the first fallback
+    -- if there are no modifiers
+    dprintf('Deriving %s from %s', hl, hldef[1])
+    vim.api.nvim_set_hl(0, hl, {default = true, link = hldef[1] })
+  else
+    dprintf('Could not derive %s', hl)
+  end
 end
 
 -- Setup a GitSign* highlight by deriving it from other potentially present