avoid array index out-of-bounds

UBSAN gave "runtime error: index 13 out of bounds for type 'const uint32_t [10]'"

include/rapidjson/internal/dtoa.h

@@ -102,7 +102,8 @@ inline void DigitGen(const DiyFp& W, const DiyFp& Mp, uint64_t delta, char* buff
         kappa--;
         if (p2 < delta) {
             *K += kappa;
-            GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * kPow10[-static_cast<int>(kappa)]);
+            int index = -static_cast<int>(kappa);
+            GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * (index < 9 ? kPow10[-static_cast<int>(kappa)] : 0));
             return;
         }
     }

test/unittest/dtoatest.cpp

@@ -37,6 +37,7 @@ TEST(dtoa, normal) {
     TEST_DTOA(1.2345678, "1.2345678");
     TEST_DTOA(0.123456789012, "0.123456789012");
     TEST_DTOA(1234567.8, "1234567.8");
+    TEST_DTOA(-79.39773355813419, "-79.39773355813419");
     TEST_DTOA(0.000001, "0.000001");
     TEST_DTOA(0.0000001, "1e-7");
     TEST_DTOA(1e30, "1e30");