fix: do not try to compute hash for frontend folders

[mcollovati]

Fixes an error in Flow tests with frontend files importing a folder instead of a file.

[mcollovati]

Fixes the following error spot in Flow tests, that however does not block the build

[main] ERROR com.vaadin.flow.server.frontend.BundleValidationUtil - Error when checking if a development bundle build is needed
java.io.IOException: Is a directory
        at java.base/sun.nio.ch.UnixFileDispatcherImpl.read0(Native Method)
        at java.base/sun.nio.ch.UnixFileDispatcherImpl.read(UnixFileDispatcherImpl.java:51)
        at java.base/sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:340)
        at java.base/sun.nio.ch.IOUtil.read(IOUtil.java:306)
        at java.base/sun.nio.ch.IOUtil.read(IOUtil.java:283)
        at java.base/sun.nio.ch.FileChannelImpl.read(FileChannelImpl.java:234)
        at java.base/sun.nio.ch.ChannelInputStream.read(ChannelInputStream.java:74)
        at java.base/sun.nio.ch.ChannelInputStream.read(ChannelInputStream.java:103)
        at java.base/java.nio.file.Files.read(Files.java:3237)
        at java.base/java.nio.file.Files.readAllBytes(Files.java:3288)
        at java.base/java.nio.file.Files.readString(Files.java:3359)
        at java.base/java.nio.file.Files.readString(Files.java:3318)
        at com.vaadin.flow.server.frontend.BundleValidationUtil.frontendImportsFound(BundleValidationUtil.java:726)
        at com.vaadin.flow.server.frontend.BundleValidationUtil.needsBuildInternal(BundleValidationUtil.java:266)
        at com.vaadin.flow.server.frontend.BundleValidationUtil.needsBuildDevBundle(BundleValidationUtil.java:181)Listening for transport dt_socket at address: 8000

        at com.vaadin.flow.server.frontend.BundleValidationUtil.needsBuild(BundleValidationUtil.java:106)
        at com.vaadin.flow.server.frontend.NodeTasks.<init>(NodeTasks.java:159)
        at com.vaadin.base.devserver.startup.DevModeInitializer.initDevModeHandler(DevModeInitializer.java:318)
        at com.vaadin.base.devserver.DevModeHandlerManagerImpl.initDevModeHandler(DevModeHandlerManagerImpl.java:104)
        at com.vaadin.base.devserver.startup.DevModeStartupListener.initialize(DevModeStartupListener.java:83)

[sonarqubecloud]

Quality Gate passed

Issues
2551 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

1 315 files  ± 0  1 315 suites  ±0   1h 14m 23s ⏱️ -27s
9 328 tests ± 0  9 260 ✅ ± 0  68 💤 ±0  0 ❌ ±0 
9 788 runs  +12  9 712 ✅ +12  76 💤 ±0  0 ❌ ±0 

Results for commit 4639513. ± Comparison against base commit d4fca88.

♻️ This comment has been updated with latest results.