Fixed warnings in PJLIB string_i.h about variable may not get initialized

git-svn-id: https://svn.pjsip.org/repos/pjproject/trunk@1527 74dad513-b988-da41-8d7b-12977e46ad98
diff --git a/pjlib/include/pj/string_i.h b/pjlib/include/pj/string_i.h
index 1590b04..b5308a3 100644
--- a/pjlib/include/pj/string_i.h
+++ b/pjlib/include/pj/string_i.h
@@ -194,6 +194,7 @@
 	copy2.ptr = (char*)str2;
 	copy2.slen = pj_ansi_strlen(str2);
     } else {
+	copy2.ptr = NULL;
 	copy2.slen = 0;
     }
 
@@ -297,6 +298,7 @@
 	copy2.ptr = (char*)str2;
 	copy2.slen = pj_ansi_strlen(str2);
     } else {
+	copy2.ptr = NULL;
 	copy2.slen = 0;
     }