oss-fuzzshark: force direct malloc

Set two environment variables (needs to be done before epan_init and
before the first g_slice_alloc call) to force direct memory allocation
without another layer that could hide bugs.

Change-Id: I0d72092c239e2e7f42b0b7849c01471407e785e2
Reviewed-on: https://code.wireshark.org/review/21195
Reviewed-by: Michael Mann <mmann78@netscape.net>

tools/oss-fuzzshark/fuzzshark.c

@@ -146,6 +146,9 @@ fuzz_init(int argc _U_, char **argv)
 	dissector_handle_t fuzz_handle = NULL;
 #endif
 
+	setenv("WIRESHARK_DEBUG_WMEM_OVERRIDE", "simple", 0);
+	setenv("G_SLICE", "always-malloc", 0);
+
 	cmdarg_err_init(failure_warning_message, failure_message_cont);
 
 	/*