[NTI] Do a null check to avoid a crash related to loose function types.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135169906

src/com/google/javascript/jscomp/NewTypeInference.java

@@ -3196,7 +3196,14 @@ private EnvTypePair analyzeLooseCallNodeFwd(
     // Unsound if the arguments and callee have interacting side effects
     EnvTypePair calleePair = analyzeExprFwd(
         callee, tmpEnv, commonTypes.topFunction(), looseFunctionType);
-    JSType result = calleePair.type.getFunTypeIfSingletonObj().getReturnType();
+    FunctionType calleeType = calleePair.type.getFunTypeIfSingletonObj();
+    if (calleeType == null) {
+      // TODO(dimvar): There is no unit test for this. We have only seen it
+      // happen in large programs. Normally, calleeType shouldn't be null.
+      // Revisit later to find cause.
+      return new EnvTypePair(calleePair.env, requiredType);
+    }
+    JSType result = calleeType.getReturnType();
     return new EnvTypePair(calleePair.env,
         isImpreciseType(result) ? requiredType : result);
   }