bash memory leak in read.

==21107== 524 bytes in 44 blocks are definitely lost in loss record 1 of 4
==21107==    at 0x4905E7B: malloc (in /usr/lib64/valgrind/amd64-linux/vgpreload_memcheck.so)
==21107==    by 0x455FAA: xmalloc (in /bin/bash)
==21107==    by 0x450F0E: substring (in /bin/bash)
==21107==    by 0x43A9B3: (within /bin/bash)
==21107==    by 0x43ABCC: get_word_from_string (in /bin/bash)
==21107==    by 0x45EC7B: read_builtin (in /bin/bash)
==21107==    by 0x42731D: (within /bin/bash)
==21107==    by 0x42ACBC: (within /bin/bash)
==21107==    by 0x429211: execute_command_internal (in /bin/bash)
==21107==    by 0x42798E: execute_command (in /bin/bash)
==21107==    by 0x428A32: (within /bin/bash)
==21107==    by 0x4296E2: execute_command_internal (in /bin/bash)