[automerger] Fix overflow/dos in 3gg text description parsing am: 851e22d1dc am: efeff07750 am: 93e7dd1e8b am: 0d6a0e7d88 am: ec9f664d7b am: 806e1cbf2f am: e44b6c7854 am: 6ea9da936b am: c17a483a1f
am: 34b9e0b641

Change-Id: I858eb16bd78770bf88b33cbbd03edd2442669604