Fix NPE in JavaNullabilityChecker when checking equals-calls

This NPE was introduced in ce41b5745a
Prior to the latter change there was a synthetic PSI element for each
equals-related call, thus callOperationNode was not null here.

== are intentionally treated as safe calls, but for nullability checker
it's not relevant, it only should report warnings on real safe-calls

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/checkers/JavaNullabilityChecker.kt

@@ -109,8 +109,9 @@ class JavaNullabilityChecker : AdditionalTypeChecker {
         }
 
         if (safeAccess) {
+            val safeAccessElement = c.call.callOperationNode?.psi ?: return
             doIfNotNull(receiverArgument.type, { dataFlowValue }, c) {
-                c.trace.report(Errors.UNNECESSARY_SAFE_CALL.on(c.call.callOperationNode!!.psi, receiverArgument.type))
+                c.trace.report(Errors.UNNECESSARY_SAFE_CALL.on(safeAccessElement, receiverArgument.type))
             }
 
             return