8323078: Incorrect length argument to g_utf8_strlen in pango.c

Submitted upstream: <https://github.com/openjdk/jfx/pull/1320>

diff --git a/modules/javafx.graphics/src/main/native-font/pango.c b/modules/javafx.graphics/src/main/native-font/pango.c
index 4cd8a9321a552f2f..3141c42da708e8a7 100644
--- a/modules/javafx.graphics/src/main/native-font/pango.c
+++ b/modules/javafx.graphics/src/main/native-font/pango.c
@@ -402,7 +402,7 @@ JNIEXPORT jlong JNICALL OS_NATIVE(g_1utf8_1strlen)
     (JNIEnv *env, jclass that, jlong str, jlong pos)
 {
     if (!str) return 0;
-    return (jlong)g_utf8_strlen((const gchar *)str, (const gchar *)pos);
+    return (jlong)g_utf8_strlen((const gchar *)str, (gssize)pos);
 }
 
 JNIEXPORT jlong JNICALL OS_NATIVE(g_1utf16_1to_1utf8)