fix: handle null passed to SvgLength (#1903)

SvgLength from method should be able to parse null since it is a correct value, we then use the empty constructor since it provides default values.

android/src/main/java/com/horcrux/svg/SVGLength.java

@@ -104,11 +104,11 @@ class SVGLength {
   }
 
   static SVGLength from(String string) {
-    return new SVGLength(string);
+    return string != null ? new SVGLength(string) : new SVGLength();
   }
 
   static SVGLength from(Double value) {
-    return new SVGLength(value);
+    return value != null ? new SVGLength(value) : new SVGLength();
   }
 
   static String toString(Dynamic dynamic) {