Fix short flags being consumed as string values

[datduyng]

A string-valued short flag could incorrectly consume the next short flag as its value. Here, -m expects a match string while -v is a separate boolean flag.

> @const list -m -v

Input:
  -m -> expects a string value
  -v -> verbose boolean flag

Before:
  parsed match -> "-v"
  parsed verbose -> false
  output -> no result

After:
  -v is recognized as another flag, leaving -m without a value
  output -> Missing value for flag '-m'

The short-flag check used an impossible condition (character < "0" && character > "9"). Changing it to || rejects unquoted flag tokens as string values while still allowing negative numeric values such as -1 and quoted values such as '-v'.

pr-2712-before-after.mp4

[datduyng]

pr-2712-before-after.mp4