BUG: BMPImageIO buffer size computation.

Fix valgrind detected Invalid Pointer Write errors.  The use of
paddedStreamRead must come after is computed for all cases.

Co-authored-by: Bill Lorensen <bill.lorensen@gmail.com>

Change-Id: I003c4edbee03c8e15fd2c083c93cb8239dee67ef
Merge topic 'BMP-invalid-pointer-write'

0beb0ed BUG: BMPImageIO buffer size computation.