fix: avoid invalid option '%-100' to 'format' and similar

As described in the related issue, I didn't have a reliable repro, but I
have seen this error message on occasion:

> Error executing lua callback:
> ...command-t/lua/wincent/commandt/private/match_listing.lua:65:
> invalid option '%-100' to 'format'

I first suspected a bad cached value, and that may be the case, but
either way, the arithmetic here seems off, as it will allow a bad format
to occur whenever `width` is, say, 103 (`width` usually comes from
a `Window` instance, with `vim.o.columns` used as a fallback).

I was finally able to repro by setting `margin` to `1` and then
adjusting my window size until `'columns'` was (I think) 107.

Closes: #415

Author: wincent

lua/wincent/commandt/private/match_listing.lua

@@ -57,13 +57,11 @@ local format_line = function(line, width, selected)
     :gsub('\v', '\\v')
 
   -- Right pad so that selection highlighting is shown across full width.
-  if width < 104 then
-    if #line > 99 then
-      -- No padding needed.
-      line = prefix .. line
-    else
-      line = prefix .. string.format('%-' .. (width - #prefix) .. 's', line)
-    end
+  if width < 102 and #line > 99 then
+    -- No padding needed.
+    line = prefix .. line
+  elseif width < 102 then
+    line = prefix .. string.format('%-' .. (width - #prefix) .. 's', line)
   else
     -- Avoid: "invalid option" caused by format argument > 99.
     line = prefix .. string.format('%-99s', line)