AndroidTarget: fix ps()

ps() splits the output on whiestspace into fields; always expecting
nine. In some cases, wchan field may be blank, resulting in only eight
chunks after the split. Detect that case and insert and empty entry at
the appropriate index.
diff --git a/devlib/target.py b/devlib/target.py
index fca798c..4b2da42 100644
--- a/devlib/target.py
+++ b/devlib/target.py
@@ -1024,8 +1024,12 @@
         result = []
         for line in lines:
             parts = line.split(None, 8)
-            if parts:
-                result.append(PsEntry(*(parts[0:1] + map(int, parts[1:5]) + parts[5:])))
+            if not parts:
+                continue
+            if len(parts) == 8:
+                # wchan was blank; insert an empty field where it should be.
+                parts.insert(5, '')
+            result.append(PsEntry(*(parts[0:1] + map(int, parts[1:5]) + parts[5:])))
         if not kwargs:
             return result
         else: