[DebugInfo] Fix infinite loop caused by reading past debug_line end

If the claimed unit length of a debug line program is such that the line
table would finish past the end of the .debug_line section, an infinite
loop occurs because the data extractor will continue to "read" zeroes
without changing the offset. This previously didn't hit an error because
the line table program handles a series of zeroes as a bad extended
opcode.

This patch fixes the inifinite loop and adds a warning if the program
doesn't fit in the available data.

Reviewed by: JDevlieghere

Differential Revision: https://reviews.llvm.org/D72279