perf: optimize handling of font properties in G elements

__tests__/__snapshots__/css.test.tsx.snap

@@ -155,13 +155,9 @@ exports[`supports CSS in style element 1`] = `
 </svg>"
   xmlns="http://www.w3.org/2000/svg"
 >
-  <RNSVGGroup
-    font={Object {}}
-  >
+  <RNSVGGroup>
     <RNSVGDefs />
-    <RNSVGGroup
-      font={Object {}}
-    >
+    <RNSVGGroup>
       <RNSVGRect
         fill={4294901760}
         height={200}
@@ -179,9 +175,7 @@ exports[`supports CSS in style element 1`] = `
         y={0}
       />
     </RNSVGGroup>
-    <RNSVGGroup
-      font={Object {}}
-    >
+    <RNSVGGroup>
       <RNSVGRect
         fill={4294901760}
         fillOpacity={0.3}

src/elements/G.tsx

@@ -24,16 +24,24 @@ export default class G<P> extends Shape<P> {
   render() {
     const { props } = this;
     const prop = propsAndStyles(props);
+    const extractedProps = extractProps(prop, this);
+    const font = extractFont(prop);
+    if (hasProps(font)) {
+      extractedProps.font = font;
+    }
     return (
-      <RNSVGGroup
-        ref={this.refMethod}
-        {...extractProps(prop, this)}
-        font={extractFont(prop)}
-      >
+      <RNSVGGroup ref={this.refMethod} {...extractedProps}>
         {props.children}
       </RNSVGGroup>
     );
   }
 }
 
+const hasProps = (obj: {}) => {
+  for (let _ in obj) {
+    return true;
+  }
+  return false;
+};
+
 export const RNSVGGroup = requireNativeComponent('RNSVGGroup');