fix(VFileInput, VFileUpload): avoid invalid accept when not defined

fixes #22131

Author: J-Sek

packages/vuetify/src/components/VFileInput/VFileInput.tsx

@@ -239,7 +239,8 @@ export const VFileInput = genericComponent<VFileInputSlots>()({
       }
 
       const expectsDirectory = attrs.webkitdirectory !== undefined && attrs.webkitdirectory !== false
-      const inputAccept = expectsDirectory ? undefined : (props.filterByType ?? String(attrs.accept))
+      const acceptFallback = attrs.accept ? String(attrs.accept) : undefined
+      const inputAccept = expectsDirectory ? undefined : (props.filterByType ?? acceptFallback)
 
       return (
         <VInput

packages/vuetify/src/labs/VFileUpload/VFileUpload.tsx

@@ -192,7 +192,8 @@ export const VFileUpload = genericComponent<VFileUploadSlots>()({
       const [rootAttrs, inputAttrs] = filterInputAttrs(attrs)
 
       const expectsDirectory = attrs.webkitdirectory !== undefined && attrs.webkitdirectory !== false
-      const inputAccept = expectsDirectory ? undefined : (props.filterByType ?? String(attrs.accept))
+      const acceptFallback = attrs.accept ? String(attrs.accept) : undefined
+      const inputAccept = expectsDirectory ? undefined : (props.filterByType ?? acceptFallback)
 
       const inputNode = (
         <input