Fix llvm error: variables may be used uninitialized

Signed-off-by: Sergey <sergio_nsk@yahoo.de>
diff --git a/library/ssl_cache.c b/library/ssl_cache.c
index 7c16e10..8b82297 100644
--- a/library/ssl_cache.c
+++ b/library/ssl_cache.c
@@ -246,7 +246,7 @@
     mbedtls_ssl_cache_context *cache = (mbedtls_ssl_cache_context *) data;
     mbedtls_ssl_cache_entry *cur;
 
-    size_t session_serialized_len;
+    size_t session_serialized_len = 0;
     unsigned char *session_serialized = NULL;
 
 #if defined(MBEDTLS_THREADING_C)