DWARF-5: Ignore empty range in DWARF-5 line number tables

The DWARF5 spec does indeed explicitly say: "A bounded range entry whose
beginning and ending address offsets are equal (including zero) indicates
an empty range and may be ignored."

Since arange_add already ignores empty ranges, remove the whole check
which is equivalent to the check plus explicit continue.

	PR binutils/27231
	* dwarf2.c (read_rnglists): Ignore empty range when parsing line
	number tables.