Call to malloc() without checking for error return.

[ywkaras]

https://github.com/SolidWallOfCode/libswoc/blob/master/code/src/MemArena.cc#L97

[ywkaras]

Proposed fix: https://github.com/ywkaras/trafficserver/blob/malloc/lib/swoc/src/MemArena.cc#L98