Fix DataConverter ConverterParticleToNBT.parseProperties

- The old code was using `StringReader.peek()` in a place where it meant to be `StringReader.skip()`.
- The vanilla code allows a trailing comma, but only if there is no whitespace between it and the closing bracket, which is a bit weird. I think that's a bug and it shouldn't allow trailing commas, but if you disagree then only the first issue needs to be fixed.

patches/server/Rewrite-dataconverter-system.patch

@@ -7970,9 +7970,8 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +            reader.expect('[');
 +            reader.skipWhitespace();
 +
-+            while (reader.canRead() && reader.peek() != ']') {
-+                reader.skipWhitespace();
-+
++            if (reader.canRead() && reader.peek() != ']') {
++                while (reader.canRead()) {
 +                    final String property = reader.readString();
 +    
 +                    reader.skipWhitespace();
@@ -7990,7 +7989,10 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +                        }
 +    
 +                        // skip ',' and move onto next entry
-+                    reader.peek();
++                        reader.skip();
++                    }
++                    
++                    reader.skipWhitespace();
 +                }
 +            }
 +