[SPARK-21826][SQL] outer broadcast hash join should not throw NPE

## What changes were proposed in this pull request?

This is a bug introduced by https://github.com/apache/spark/pull/11274/files#diff-7adb688cbfa583b5711801f196a074bbL274 .

Non-equal join condition should only be applied when the equal-join condition matches.

## How was this patch tested?

regression test

Author: Wenchen Fan <wenchen@databricks.com>

Closes #19036 from cloud-fan/bug.

sql/core/src/main/scala/org/apache/spark/sql/execution/joins/BroadcastHashJoinExec.scala

@@ -283,8 +283,8 @@ case class BroadcastHashJoinExec(
       s"""
          |boolean $conditionPassed = true;
          |${eval.trim}
-         |${ev.code}
          |if ($matched != null) {
+         |  ${ev.code}
          |  $conditionPassed = !${ev.isNull} && ${ev.value};
          |}
        """.stripMargin

sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala

@@ -17,6 +17,7 @@
 
 package org.apache.spark.sql
 
+import scala.collection.JavaConverters._
 import scala.collection.mutable.ListBuffer
 import scala.language.existentials
 
@@ -26,6 +27,7 @@ import org.apache.spark.sql.catalyst.analysis.UnresolvedRelation
 import org.apache.spark.sql.execution.joins._
 import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.test.SharedSQLContext
+import org.apache.spark.sql.types.StructType
 
 class JoinSuite extends QueryTest with SharedSQLContext {
   import testImplicits._
@@ -767,4 +769,22 @@ class JoinSuite extends QueryTest with SharedSQLContext {
       }
     }
   }
+
+  test("outer broadcast hash join should not throw NPE") {
+    withTempView("v1", "v2") {
+      withSQLConf(SQLConf.WHOLESTAGE_CODEGEN_ENABLED.key -> "true") {
+        Seq(2 -> 2).toDF("x", "y").createTempView("v1")
+
+        spark.createDataFrame(
+          Seq(Row(1, "a")).asJava,
+          new StructType().add("i", "int", nullable = false).add("j", "string", nullable = false)
+        ).createTempView("v2")
+
+        checkAnswer(
+          sql("select x, y, i, j from v1 left join v2 on x = i and y < length(j)"),
+          Row(2, 2, null, null)
+        )
+      }
+    }
+  }
 }