Fix overflow sanitizer in Visualizer_command.

There's an intended integer overflow in the Visualizer_command function.
This refactors it to use the builtin overflow-safe function.

 runtime error: unsigned integer overflow: 1664 - 4048 cannot be
 represented in type 'unsigned int'

Bug: 30969751
Test: Builds and boots.
Change-Id: I63a505f4b073480f52d0b073ec5e45c52212caa8