Fix divide by zero

New version can return page size of zero, seems to be when empty

Author: castortech

mdbxjni/src/main/java/com/castortech/mdbxjni/Env.java

@@ -524,6 +524,11 @@ public Stat stat() {
 	public float percentageFull() {
 		Stat stat2 = stat();
 		EnvInfo info2 = info();
+
+		if (stat2.ms_psize == 0) {
+			return 0.0f;
+		}
+
 		long nbrPages = info2.getMapSize() / stat2.ms_psize;
 		return (info2.getLastPgNo() / (float)nbrPages) * 100;
 	}