[DebugInfo] Prevent crash when .debug_line line_range is zero

The line_range value of a debug line program header is used in divisions
related to special opcodes and DW_LNS_const_add_pc opcodes. As such, a
value of 0 cannot be used. This change introduces a new warning, if such
a situation is identified, and does not perform the relevant
calculations.

Reviewed by: probinson, aprantl

Differential Revision: https://reviews.llvm.org/D43470