Filter kapt generate stubs classpath for non-existent entries (KT-37241)

Issue #KT-37241 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/Kapt3IT.kt

@@ -541,7 +541,7 @@ open class Kapt3IT : Kapt3BaseIT() {
     }
 
     @Test
-    fun testKt19179() {
+    fun testKt19179andKt37241() {
         val project = Project("kt19179", directoryPrefix = "kapt2")
 
         project.build("build") {
@@ -565,6 +565,9 @@ open class Kapt3IT : Kapt3BaseIT() {
                 ":app:kaptGenerateStubsKotlin",
                 ":app:kaptKotlin"
             )
+
+            // Test for KT-37241, check the that non-existent classpath entry is filtered out:
+            assertNotContains("Classpath entry points to a non-existent location")
         }
 
         project.projectDir.getFileByName("Test.kt").modify { text ->

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kapt2/kt19179/api/build.gradle

@@ -1,4 +1,5 @@
 apply plugin: 'kotlin'
+apply plugin: 'java-library'
 
 dependencies {
     compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/kapt/KaptGenerateStubsTask.kt

@@ -92,7 +92,7 @@ open class KaptGenerateStubsTask : KotlinCompile() {
         args.pluginOptions = (pluginOptionsWithKapt.arguments + args.pluginOptions!!).toTypedArray()
 
         args.verbose = project.hasProperty("kapt.verbose") && project.property("kapt.verbose").toString().toBoolean() == true
-        args.classpathAsList = this.compileClasspath.toList()
+        args.classpathAsList = this.compileClasspath.filter { it.exists() }.toList()
         args.destinationAsFile = this.destinationDir
     }