Use double type to improve floating point accuracy.

src/tags_int.cpp

@@ -2612,7 +2612,7 @@ std::ostream& print0x0007(std::ostream& os, const Value& value, const ExifData*)
     }
     std::ostringstream oss;
     oss.copyfmt(os);
-    const double t = 3600 * value.toFloat(0) + 60 * value.toFloat(1) + value.toFloat(2);
+    const double t = 3600.0 * value.toFloat(0) + 60.0 * value.toFloat(1) + value.toFloat(2);
     enforce<std::overflow_error>(std::isfinite(t), "Non-finite time value");
     int p = 0;
     const double fraction = std::fmod(t, 1);