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)