Require a space after the unit in a .in invocation

[dpk]

18:46:12 <+dpk> .in 1h30 18:46:12 <+saxo> dpk: Will remind at 23 Apr 2021 17:46:12 UTC

[… somewhat later …]

19:46:12 <+saxo> dpk: 30 19:46:32 <+dpk> sbp: qmebs require a space after the final unit? 19:46:54 <+dpk> i'd be fine with an error message telling me i have to put the m explicitly 19:47:17 <+dpk> but sending me a message in 1 hour with the text '30' is an interpretation nobody wants