fixed PY-2970 Join 2 if's intention alters behavior of code

python/src/com/jetbrains/python/codeInsight/intentions/PyJoinIfIntention.java

@@ -45,7 +45,8 @@ public class PyJoinIfIntention extends BaseIntentionAction {
     if (outer != null) {
       if (outer.getElsePart() != null || outer.getElifParts().length > 0) return false;
       PyStatement firstStatement = getFirstStatement(outer);
-
+      PyStatementList outerStList = outer.getIfPart().getStatementList();
+      if (outerStList != null && outerStList.getStatements().length != 1) return false;
       if (firstStatement instanceof PyIfStatement) {
         final PyIfStatement inner = (PyIfStatement)firstStatement;
         if (inner.getElsePart() != null || inner.getElifParts().length > 0) return false;

python/testData/intentions/beforeJoinIfMultiStatements.py

@@ -0,0 +1,16 @@
+class A:
+  def __init__(self, *args, **kwargs):
+    self.uses_remaining_this_turn = None
+    self.effects = None
+
+  def foo(self):
+    if self.can_act<caret>ivate():
+      if self.effect_queue is None:
+        self.effect_queue = list(self.effects)
+      for effect in self.effect_queue:
+        effect.activate(source, targets)
+      self.effect_queue = None
+      self.uses_remaining_this_turn -= 1
+
+  def can_activate(self):
+    pass

python/testSrc/com/jetbrains/python/PyIntentionTest.java

@@ -125,6 +125,10 @@ public class PyIntentionTest extends PyLightFixtureTestCase {
     doNegativeTest(PyBundle.message("INTN.join.if.text"));
   }
 
+  public void testJoinIfMultiStatements() {           //PY-2970
+    doNegativeTest(PyBundle.message("INTN.join.if.text"));
+  }
+
   public void testDictConstructorToLiteralForm() {
     doTest(PyBundle.message("INTN.convert.dict.constructor.to.dict.literal"));
   }