BitSetIterator_unittest: fix an unreachable code warning

Because gtest's FAIL macro does a return, MSVC complained that the
update part of a range-based for loop was unreachable. Fixed this by
having a boolean value set to true if we execute the loop body.

BUG=angleproject:929

Change-Id: I6c1fec7ed6cf1a3aba6f02b68c1015bee2feebfd
Reviewed-on: https://chromium-review.googlesource.com/296730
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>

src/common/BitSetIterator_unittest.cpp

@@ -49,11 +49,15 @@ TEST_F(BitSetIteratorTest, Iterator)
 // Test an empty iterator.
 TEST_F(BitSetIteratorTest, EmptySet)
 {
+    // We don't use the FAIL gtest macro here since it returns immediately,
+    // causing an unreachable code warning in MSVS
+    bool sawBit = false;
     for (unsigned long bit : IterateBitSet(mStateBits))
     {
+        sawBit = true;
         UNUSED_TRACE_VARIABLE(bit);
-        FAIL() << "Should not be reached";
     }
+    EXPECT_FALSE(sawBit);
 }
 
 // Test iterating a result of combining two bitsets.