Don’t crash when scanning candidate matching the prefix

packages/tailwindcss/src/candidate.ts

@@ -229,7 +229,7 @@ export function* parseCandidate(input: string, designSystem: DesignSystem): Iter
   // A prefix is a special variant used to prefix all utilities. When present,
   // all utilities must start with that variant which we will then remove from
   // the variant list so no other part of the codebase has to know about it.
-  if (designSystem.theme.prefix) {
+  if (designSystem.theme.prefix && rawVariants.length > 1) {
     if (rawVariants[0] !== designSystem.theme.prefix) return null
 
     rawVariants.shift()

packages/tailwindcss/src/prefix.test.ts

@@ -333,3 +333,19 @@ test('a prefix must be letters only', async () => {
     `[Error: The prefix "__" is invalid. Prefixes must be lowercase ASCII letters (a-z) only.]`,
   )
 })
+
+test('a candidate matching the prefix does not crash', async () => {
+  let input = css`
+    @theme reference prefix(tomato);
+    @tailwind utilities;
+  `
+
+  let compiler = await compile(input)
+
+  expect(compiler.build(['tomato', 'tomato:flex'])).toMatchInlineSnapshot(`
+    ".tomato\\:flex {
+      display: flex;
+    }
+    "
+  `)
+})