Fix carry in fallback_format

include/fmt/format-inl.h

@@ -2545,7 +2545,7 @@ void fallback_format(Double d, int num_digits, bool binary32, buffer<char>& buf,
         ++buf[i - 1];
       }
       if (buf[0] == overflow) {
-        buf[0] = '0';
+        buf[0] = '1';
         ++exp10;
       }
       return;

test/format-test.cc

@@ -957,6 +957,7 @@ TEST(FormatterTest, Precision) {
   EXPECT_EQ("1.23", format("{:.02f}", 1.234));
   EXPECT_EQ("0.001", format("{:.1g}", 0.001));
   EXPECT_EQ("1019666400", format("{}", 1019666432.0f));
+  EXPECT_EQ("1e+01", format("{:.0e}", 9.5));
 
   EXPECT_THROW_MSG(format("{0:.2}", reinterpret_cast<void*>(0xcafe)),
                    format_error,