fix(highlight): check the return value of nvim_get_hl()

See #260.

Author: ggandor

fnl/leap/highlight.fnl

@@ -150,9 +150,13 @@ so we set a temporary highlight on it to see where we are."
     (let [normal (vim.api.nvim_get_hl 0 {:name "Normal" :link false})
           label* (vim.api.nvim_get_hl 0 {:name self.group.label :link false})]
       ; E.g., the old default color scheme (`vim`) does not define Normal at all.
-      (when (and label*.bg normal.bg)
+      ; Also, `nvim_get_hl()` apparently does not guarantee to return numeric
+      ; values in the table (#260).
+      (when (and (= (type label*.bg) "number")
+                 (= (type normal.bg) "number"))
         (set label*.bg (blend label*.bg normal.bg 0.7)))
-      (when (and label*.fg normal.fg)
+      (when (and (= (type label*.fg) "number")
+                 (= (type normal.fg) "number"))
         (set label*.fg (blend label*.fg normal.bg 0.5)))
       (vim.api.nvim_set_hl 0 self.group.label-dimmed label*))))