Add fuzz targets

Fuzzing is something that's good to do for a general purpose library and
can find bugs relatively quickly.

Enable fuzzing with libfuzzer (selected only because it was the easiest
to set up) and enable fuzz targets for 3 of our buffer-based interfaces.

Change-Id: I695a3a60ba09bea92cd462566bf2c46337eabd4b
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/base64.c b/base64.c
index 38ea0ab..5ed39c6 100644
--- a/base64.c
+++ b/base64.c
@@ -20,6 +20,10 @@
 	const UINT8 *src_end;
 	const UINT8 *in_pos;
 
+	if (len <= 0) {
+		return NULL;
+	}
+
 	if (!out_len) {
 		return NULL;
 	}