Fix leak of range_list (see below an example) in readdwarf3.c.

Fix leak of range_list (see below an example) in readdwarf3.c.
(found by running regression tests with an outer memcheck).

(validated by running all regression tests "natively" on x86 and amd64,
and re-running regressions tests with outer memcheck).

==7500== 160 bytes in 2 blocks are definitely lost in loss record 75 of 246
==7500==    at 0x2803CEF7: vgPlain_arena_malloc (m_mallocfree.c:1599)
==7500==    by 0x280AAFA5: vgModuleLocal_dinfo_zalloc (misc.c:48)
==7500==    by 0x2804E2A4: vgPlain_newXA (m_xarray.c:68)
==7500==    by 0x280B3CD6: unitary_range_list (readdwarf3.c:703)
==7500==    by 0x280B66CF: parse_var_DIE (readdwarf3.c:1631)
==7500==    by 0x280BA0A6: read_DIE (readdwarf3.c:3248)
==7500==    by 0x280BA170: read_DIE (readdwarf3.c:3269)
==7500==    by 0x280BABC4: T.364 (readdwarf3.c:3611)
==7500==    by 0x280BC634: vgModuleLocal_new_dwarf3_reader (readdwarf3.c:4035)
==7500==    by 0x280609F4: vgModuleLocal_read_elf_debug_info (readelf.c:2529)
==7500==    by 0x2805BD31: vgPlain_di_notify_mmap (debuginfo.c:610)
==7500==    by 0x280362E3: valgrind_main (m_main.c:1944)

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@12419