Check for out of memory when allocating sqlca.

src/interfaces/ecpg/compatlib/informix.c

src/interfaces/ecpg/ecpglib/connect.c

src/interfaces/ecpg/ecpglib/data.c

src/interfaces/ecpg/ecpglib/descriptor.c

src/interfaces/ecpg/ecpglib/error.c

src/interfaces/ecpg/ecpglib/execute.c

src/interfaces/ecpg/ecpglib/misc.c