[DWARF][Verifier] Do not add child DieRangeInfo with empty address range to the parent.

verifyDieRanges function checks for the intersected address ranges.
It adds child DieRangeInfo into parent DieRangeInfo to check
whether children have overlapping address ranges. It is safe to not add
DieRangeInfo with empty address range into parent's children list.
This decreases the number of children which should be navigated and as a result
decreases execution time(parents having a lot of children with empty ranges
spend much time navigating them). For this command: "llvm-dwarfdump --verify clang-repl"
execution time decreased from 220 sec till 75 sec.

Differential Revision: https://reviews.llvm.org/D107554