Never produce -0 when evaluating expressions (like -"")

Fix for #1085. The major case was already there, but more expressions can result in -0.

lib/compress.js

@@ -1029,9 +1029,9 @@ merge(Compressor.prototype, {
               case "void": return void ev(e, compressor);
               case "~": return ~ev(e, compressor);
               case "-":
-                e = ev(e, compressor);
-                if (e === 0) throw def;
-                return -e;
+                e = -ev(e, compressor);
+                if (e === -0) throw def;
+                return e;
               case "+": return +ev(e, compressor);
             }
             throw def;

test/compress/evaluate.js

@@ -0,0 +1,9 @@
+negative_zero: {
+    options = { evaluate: true }
+    input: {
+        assert.sameValue(-"", -0, '-""');
+    }
+    expect: {
+        assert.sameValue(-"", -0, '-""');
+    }
+}