transfer: fix amount validation regexp

pages/Transfer.qml

@@ -146,7 +146,7 @@ Rectangle {
                       inlineButton.onClicked: amountLine.text = "(all)"
 
                       validator: RegExpValidator {
-                          regExp: /(.|)(\d{1,8})([.]\d{1,12})?$/
+                          regExp: /^(\d{1,8})?([\.]\d{1,12})?$/
                       }
                   }
               }