...where bad input like "WRONG CELL NAME" (in PythonTest_sw_python's
sw/qa/python/check_xtexttable.py) could wrap around to a valid but wrong nRet.
Instead, return SAL_MAX_UINT16 upon overflow.  At least the call to GetBoxNum in
SwTable::GetTableBox (sw/source/core/table/swtable.cxx) with bFirstPart
potentially true, assigning to nBox, then later checks

  if( nBox >= pBoxes->size() )
      return nullptr;

so returning SAL_MAX_UINT16 upon overflow appears to be the best choice.

(Found with Clang's -fsanitize=implicit-signed-integer-truncation.)

Change-Id: I12822a6bd4f0269adb14c04eefbd1cde4d288728
Reviewed-on: https://gerrit.libreoffice.org/68203
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>