[SPARK-5380][GraphX] Solve an ArrayIndexOutOfBoundsException when build graph with a file format error

When I build a graph with a file format error, there will be an ArrayIndexOutOfBoundsException

Author: Leolh <leosandylh@gmail.com>

Closes #4176 from Leolh/patch-1 and squashes the following commits:

94f6d22 [Leolh] Update GraphLoader.scala
23767f1 [Leolh] [SPARK-3650][GraphX] There will be an ArrayIndexOutOfBoundsException if the format of the source file is wrong

graphx/src/main/scala/org/apache/spark/graphx/GraphLoader.scala

@@ -77,7 +77,7 @@ object GraphLoader extends Logging {
         if (!line.isEmpty && line(0) != '#') {
           val lineArray = line.split("\\s+")
           if (lineArray.length < 2) {
-            logWarning("Invalid line: " + line)
+            throw new IllegalArgumentException("Invalid line: " + line)
           }
           val srcId = lineArray(0).toLong
           val dstId = lineArray(1).toLong