newPool() allocates memory without checking for NULL

In [antlr3collections.c](https://github.com/antlr/antlr3/blob/master/runtime/C/src/antlr3collections.c), the function `newPool()` is calling both `realloc` and `malloc` without properly handling the out of memory (NULL return) case.

This ultimately leads to my application crashing in [antlr3commontoken.c](https://github.com/antlr/antlr3/blob/master/runtime/C/src/antlr3commontoken.c), in `newPoolToken()` with an access violation caused by a NULL pointer dereference.

Start in runtime/C/src/antlr3collections.c at newPool(), then inspect runtime/C/src/antlr3commontoken.c at newPoolToken() to understand the reported NULL dereference. Trace both realloc and malloc results and verify that out-of-memory returns are handled without the application crashing through a NULL pointer.

Written by the indexing model from the issue text.