Fix endless loop on importing mysql schema:

umbrello/codeimport/sqlimport.cpp
- Replace variable `index' by constant `origIndex' located inside the
  while-loop.
- In loop condition replace QLatin1String("COMMENT") by
  QLatin1String("comment").
- After end of while-loop, if token contains COMMENT then advance until
  it contains "," or ")".

BUG:398082
FIXED-IN:2.30.2 (KDE Applications 19.12.2)