Fix two PTSes tests for MESH

It is possible that setup has more than two PTSes available and invalid
check was causing those to be skipped. Follow early return pattern as
other profiles as this is future proof.

autopts/ptsprojects/mynewt/mesh.py

@@ -618,8 +618,10 @@ def test_cases(ptses):
 
         tc_list.append(instance)
 
-    if len(ptses) == 2:
-        tc_list += test_cases_slaves
-        pts2 = ptses[1]
+    if len(ptses) < 2:
+        return tc_list
+
+    tc_list += test_cases_slaves
+    pts2 = ptses[1]
 
     return tc_list

autopts/ptsprojects/zephyr/mesh.py

@@ -986,8 +986,10 @@ def test_cases(ptses):
 
         tc_list.append(instance)
 
-    if len(ptses) == 2:
-        tc_list += test_cases_slaves
-        pts2 = ptses[1]
+    if len(ptses) < 2:
+        return tc_list
+
+    tc_list += test_cases_slaves
+    pts2 = ptses[1]
 
     return tc_list