[Crash] Prevent rare crash

Author: Hugo Tunius

CHANGELOG.md

@@ -1,6 +1,8 @@
 Master
 ------
 
+* Prevent potential crash when `self.font` is `nil`. This might cause the component to render incorrectly, but it will not crash which is preferable. See [#186](https://github.com/Skyscanner/SkyFloatingLabelTextField/issues/186)
+
 v3.5.0
 ------
 

Sources/SkyFloatingLabelTextField.swift

@@ -625,7 +625,11 @@ open class SkyFloatingLabelTextField: UITextField { // swiftlint:disable:this ty
      -returns: the calculated height of the textfield. Override to size the textfield with a different height
      */
     open func textHeight() -> CGFloat {
-        return self.font!.lineHeight + 7.0
+        guard let font = self.font else {
+            return 0.0
+        }
+
+        return font.lineHeight + 7.0;
     }
 
     // MARK: - Layout