[SPARK-8400] [ML] Added check in ml.ALS for positive block size parameter setting

Added check for positive block size with a note that -1 for auto-configuring is not supported

Author: Bryan Cutler <bjcutler@us.ibm.com>

Closes #8363 from BryanCutler/ml.ALS-neg-blocksize-8400-1.3.

Author: BryanCutler

mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala

@@ -234,10 +234,16 @@ class ALS extends Estimator[ALSModel] with ALSParams {
   def setRank(value: Int): this.type = set(rank, value)
 
   /** @group setParam */
-  def setNumUserBlocks(value: Int): this.type = set(numUserBlocks, value)
+  def setNumUserBlocks(value: Int): this.type = {
+    require(value > 0, "Number of blocks must be > 0, auto-configuring with -1 is not supported.")
+    set(numUserBlocks, value)
+  }
 
   /** @group setParam */
-  def setNumItemBlocks(value: Int): this.type = set(numItemBlocks, value)
+  def setNumItemBlocks(value: Int): this.type = {
+    require(value > 0, "Number of blocks must be > 0, auto-configuring with -1 is not supported.")
+    set(numItemBlocks, value)
+  }
 
   /** @group setParam */
   def setImplicitPrefs(value: Boolean): this.type = set(implicitPrefs, value)