chore: fix double meeting creation

Ghost Userrequested to merge
(removed):2601-resolve-double-meeting-creation into main

After !1750 (merged) we had the issue of form being submit twice (for some reason only for users without any meetings).

Restructured form to only have one way to submit to avoid double requests.

Closes #2601 #opentalk/bugs#94

Edited by Michael Holst

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