Update libsrtp to 1.5.2

srtp/crypto/math/datatypes.c

Index: srtp/crypto/math/datatypes.c
diff --git a/srtp/crypto/math/datatypes.c b/srtp/crypto/math/datatypes.c
index c4af8d7e45377e75927f07c2d2486f1bff13a1cd..a30873eead055971a9689708ee12201899fc6eba 100644
--- a/srtp/crypto/math/datatypes.c
+++ b/srtp/crypto/math/datatypes.c
@@ -535,7 +535,7 @@ static const char b64chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
   "abcdefghijklmnopqrstuvwxyz0123456789+/";
 
 static int base64_block_to_octet_triple(char *out, char *in) {
-  unsigned char sextets[4] = {};
+  unsigned char sextets[4] = {0};
   int j = 0;
   int i;