It is possible, eg. for the end-of-data debug_line tag, that the address
does not correspond to an instruction address but eg. the last address
of .text. To avoid an error here, we use as a bound address the greater
known address below the given bound instead.
Some entries in .dwarf_line might span 0 instructions, because a
following entry refers to exactly the same address. An enhancement might
be to make all these addresses equivalent in the matcher.
