Fix additional transcoding assertions

Fix additional transcoding assertions

	* src/buffer.h (TO_EXTERNAL_FORMAT): Remove the bad assert (ie not
	valid in all conditions).
	* src/buffer.h (TO_INTERNAL_FORMAT): Ditto.

	* src/buffer.h (DFC_SOURCE_DATA_TO_ARGS): Do the proper assert to
	the source conversion.
	* src/buffer.h (DFC_SOURCE_C_STRING_TO_ARGS): Ditto.
	* src/buffer.h (DFC_SOURCE_LISP_OPAQUE_TO_ARGS): Ditto.

	* src/buffer.h (DFC_ALLOCA_USE_CONVERTED_DATA): Do the proper assert
	to the converted data.
	* src/buffer.h (DFC_MALLOC_USE_CONVERTED_DATA): Ditto.
	* src/buffer.h (DFC_C_STRING_ALLOCA_USE_CONVERTED_DATA): Ditto.
	* src/buffer.h (DFC_C_STRING_MALLOC_USE_CONVERTED_DATA): Ditto.
	* src/buffer.h (DFC_LISP_STRING_USE_CONVERTED_DATA): Ditto.
	* src/buffer.h (DFC_LISP_OPAQUE_USE_CONVERTED_DATA): Ditto.

	* src/alloc.c (ALLOCATE_FIXED_TYPE): Make sure to detect failed
	allocations.
	* src/alloc.c (ALLOCATE_ATOMIC_FIXED_TYPE): Ditto.
	* src/alloc.c (make_uninit_string): Make sure the uninit string is
	valid after construction.

	* src/opaque.c (make_opaque): Make sure to detect failed
	allocations even in the fatal crash scenario.

Signed-off-by: Nelson Ferreira <nelson.ferreira@ieee.org>