[SPARK-53552] Optimize substr SQL function

Author: WanKun

common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java

@@ -642,9 +642,13 @@ public UTF8String substring(final int start, final int until) {
     }
 
     int j = i;
-    while (i < numBytes && c < until) {
-      i += numBytesForFirstByte(getByte(i));
-      c += 1;
+    if (until == Integer.MAX_VALUE) {
+      i = numBytes;
+    } else {
+      while (i < numBytes && c < until) {
+        i += numBytesForFirstByte(getByte(i));
+        c += 1;
+      }
     }
 
     if (i > j) {