FFMPEGMediaPlayer: Fix mpeg seek using time_base.num 1 , time_base.den 90000

Prevent division and multiplication by zero errors in native code
after mpeg video seek caused by type truncation.

When using seek on mpeg streams the multiplication product also quickly grew beyond the maximum size of int32_t thus i had to use int64_t, else i  would only be able to seek inside the first half minute of the mpeg movie stream.

https://github.com/sgothel/jogl/pull/63