Printing negative zero in complex imag part in the right way.

Author: ppisl

graalpython/com.oracle.graal.python.test/src/tests/unittest_tags/test_complex.txt

@@ -6,6 +6,7 @@
 *ComplexTest.test_getnewargs
 *ComplexTest.test_neg
 *ComplexTest.test_negated_imaginary_literal
+*ComplexTest.test_negative_zero_repr_str
 *ComplexTest.test_overflow
 *ComplexTest.test_plus_minus_0j
 *ComplexTest.test_repr_str

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/complex/PComplex.java

@@ -91,8 +91,8 @@ public double getImag() {
     @Override
     @TruffleBoundary
     public String toString() {
-        if (Double.compare(real, 0.0) == 0) {
-            return toString(imag) + "j";
+        if (Double.compare(real, 0.0) == 0) {     
+            return Double.compare(imag, 0.0) >= 0 ?  toString(imag) + "j" : String.format("-%sj", toString(-imag));
         } else {
             String realString = toString(real);
             if (real == 0.0) {