parsers BUGFIX uninitialized variable storing number of read bytes

Fixes #777
diff --git a/src/common.c b/src/common.c
index dc96310..a35c72c 100644
--- a/src/common.c
+++ b/src/common.c
@@ -181,6 +181,10 @@
     int aux;
     int i;
 
+    if (bytes_read) {
+        (*bytes_read) = 0;
+    }
+
     c = (*input)[0];
     LY_CHECK_RET(!c, LY_EINVAL);