Fix formatting of minimal negative decimal

src/IO/WriteHelpers.h

@@ -870,14 +870,13 @@ String decimalFractional(const T & x, UInt32 scale)
 template <typename T>
 void writeText(Decimal<T> x, UInt32 scale, WriteBuffer & ostr)
 {
-    if (x.value < 0)
+    T part = DecimalUtils::getWholePart(x, scale);
+
+    if (x.value < 0 && part == 0)
     {
-        x.value *= -1;
         writeChar('-', ostr); /// avoid crop leading minus when whole part is zero
     }
 
-    T part = DecimalUtils::getWholePart(x, scale);
-
     if constexpr (std::is_same_v<T, bInt256>)
         writeText(part, ostr);
     else

tests/queries/0_stateless/01456_min_negative_decimal_formatting.reference

+-9223372036854775808

tests/queries/0_stateless/01456_min_negative_decimal_formatting.sql

+select toDecimal64(-9223372036854775808, 0);