Correct scan area size on ios

ios/Classes/QRView.swift

@@ -84,7 +84,7 @@ public class QRView:NSObject,FlutterPlatformView {
         return previewView
     }
     
-    func setDimensions(_ result: @escaping FlutterResult, width: Double, height: Double, scanArea: Double, scanAreaOffset: Double) {
+    func setDimensions(_ result: @escaping FlutterResult, width: Double, height: Double, scanAreaWidth: Double, scanAreaHeight: Double, scanAreaOffset: Double) {
         // Then set the size of the preview area.
         previewView.frame = CGRect(x: 0, y: 0, width: width, height: height)
         
@@ -103,9 +103,9 @@ public class QRView:NSObject,FlutterPlatformView {
         }
 
         // Set scanArea if provided.
-        if (scanArea != 0) {
+        if (scanAreaWidth != 0 && scanAreaHeight != 0) {
             scanner?.didStartScanningBlock = {
-                self.scanner?.scanRect = CGRect(x: Double(midX) - (scanArea / 2), y: Double(midY) - (scanArea / 2), width: scanArea, height: scanArea)
+                self.scanner?.scanRect = CGRect(x: Double(midX) - (scanAreaWidth / 2), y: Double(midY) - (scanAreaHeight / 2), width: scanAreaWidth, height: scanAreaHeight)
 
                 // Set offset if provided.
                 if (scanAreaOffset != 0) {