[search addon] Escape sequence only for \n, \r, \t and \\

When `\` is followed by any other character, it will not be
interpreted as an escape sequence, i.e. `\3` will be
interpreted as literal `\3`, not as `3`.

Fixes #5428

addon/search/search.js

@@ -78,10 +78,12 @@
  }
 
  function parseString(string) {
- return string.replace(/\\(.)/g, function(_, ch) {
+ return string.replace(/\\([nrt\\])/g, function(match, ch) {
  if (ch == "n") return "\n"
  if (ch == "r") return "\r"
- return ch
+ if (ch == "t") return "\t"
+ if (ch == "\\") return "\\"
+ return match
  })
  }