chg: fix an undefined behavior about memcpy Spot by Wez Furlong. `memcpy(x, NULL, 0)` is undefined according to [1]. [1]: https://stackoverflow.com/questions/5243012 Differential Revision: https://phab.mercurial-scm.org/D3698

Added signature for changeset 9c5ced5276d6

Added tag 4.6.1 for changeset 9c5ced5276d6

mpatch: avoid integer overflow in combine() (SEC) All the callers of this function can handle a NULL return, so that appears to be the "safe" way to report an error.

mpatch: avoid integer overflow in mpatch_decode (SEC)

mpatch: fix UB integer overflows in discard() (SEC)

mpatch: fix UB in int overflows in gather() (SEC)