KT-12628: new test for arg + something with nullable arg

(cherry picked from commit a7e4e2d)

idea/testData/quickfix/nullables/unsafeInfixCall/unsafePlus.kt

@@ -0,0 +1,4 @@
+// "Replace with safe (?.) call" "true"
+
+operator fun Int.plus(index: Int) = this
+fun fox(arg: Int?) = arg <caret>+ 42

idea/testData/quickfix/nullables/unsafeInfixCall/unsafePlus.kt.after

@@ -0,0 +1,4 @@
+// "Replace with safe (?.) call" "true"
+
+operator fun Int.plus(index: Int) = this
+fun fox(arg: Int?) = arg?.plus(42)

idea/tests/org/jetbrains/kotlin/idea/quickfix/QuickFixTestGenerated.java

@@ -6077,6 +6077,12 @@ public class QuickFixTestGenerated extends AbstractQuickFixTest {
                 String fileName = KotlinTestUtils.navigationMetadata("idea/testData/quickfix/nullables/unsafeInfixCall/unsafeInfixCall.kt");
                 doTest(fileName);
             }
+
+            @TestMetadata("unsafePlus.kt")
+            public void testUnsafePlus() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("idea/testData/quickfix/nullables/unsafeInfixCall/unsafePlus.kt");
+                doTest(fileName);
+            }
         }
     }