Correctly check if width is lte 0 in Image Optimization API (#38226)

This PR corrects a mistake where a negative number could pass, as a number greater than 0.

This is due to negative numbers being a truthy value in JS.

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)

packages/next/server/image-optimizer.ts

@@ -125,7 +125,7 @@ export class ImageOptimizerCache {
 
     const width = parseInt(w, 10)
 
-    if (!width || isNaN(width)) {
+    if (width <= 0 || isNaN(width)) {
       return {
         errorMessage: '"w" parameter (width) must be a number greater than 0',
       }

test/integration/image-optimizer/test/util.js

@@ -397,7 +397,7 @@ export function runTests(ctx) {
     )
   })
 
-  it('should fail when w is 0 or less', async () => {
+  it('should fail when w is 0', async () => {
     const query = { url: '/test.png', w: 0, q: 100 }
     const res = await fetchViaHTTP(ctx.appPort, '/_next/image', query, {})
     expect(res.status).toBe(400)
@@ -406,6 +406,15 @@ export function runTests(ctx) {
     )
   })
 
+  it('should fail when w is less than 0', async () => {
+    const query = { url: '/test.png', w: -100, q: 100 }
+    const res = await fetchViaHTTP(ctx.appPort, '/_next/image', query, {})
+    expect(res.status).toBe(400)
+    expect(await res.text()).toBe(
+      `"w" parameter (width) must be a number greater than 0`
+    )
+  })
+
   it('should fail when w is not a number', async () => {
     const query = { url: '/test.png', w: 'foo', q: 100 }
     const res = await fetchViaHTTP(ctx.appPort, '/_next/image', query, {})