Clean up how the buffer is made; flatten the if tree

MetaballsKit/Renderer.swift

@@ -193,14 +193,18 @@ public class Renderer: NSObject, MTKViewDelegate {
         guard let field = delegate?.field else {
             return
         }
+        guard let buffer = commandQueue.makeCommandBuffer() else {
+            return
+        }
+
+        var didEncode = false
+
+
+        buffer.label = "Metaballs Command Buffer"
 
         field.update()
 
-        if let buffer = commandQueue.makeCommandBuffer(),
+        if let renderPass = view.currentRenderPassDescriptor {
-           let renderPass = view.currentRenderPassDescriptor {
-            buffer.label = "Metaballs Command Buffer"
-            var didEncode = false
-
             // Render the per-pixel metaballs
             if let pipeline = pixelPipeline,
                let encoder = buffer.makeRenderCommandEncoder(descriptor: renderPass) {
@@ -230,6 +234,7 @@ public class Renderer: NSObject, MTKViewDelegate {
                 encoder.endEncoding()
                 didEncode = true
             }
+        }
 
         if didEncode, let drawable = view.currentDrawable {
             buffer.present(drawable)
@@ -237,4 +242,3 @@ public class Renderer: NSObject, MTKViewDelegate {
         buffer.commit()
     }
 }
-}