Don't try to read binary data from a non-class file

Fixes EA-59470, where a virtual file is checked to be a compiled Kotlin class
from the decompiler (which doesn't check its FileType)

compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/kotlin/KotlinBinaryClassCache.java

@@ -16,6 +16,7 @@
 
 package org.jetbrains.jet.lang.resolve.kotlin;
 
+import com.intellij.ide.highlighter.JavaClassFileType;
 import com.intellij.openapi.Disposable;
 import com.intellij.openapi.components.ServiceManager;
 import com.intellij.openapi.util.Ref;
@@ -45,6 +46,8 @@ public final class KotlinBinaryClassCache implements Disposable {
 
     @Nullable
     public static KotlinJvmBinaryClass getKotlinBinaryClass(@NotNull VirtualFile file) {
+        if (file.getFileType() != JavaClassFileType.INSTANCE) return null;
+
         KotlinBinaryClassCache service = ServiceManager.getService(KotlinBinaryClassCache.class);
         return service.cache.get().get(file).get();
     }

compiler/frontend.java/src/org/jetbrains/jet/lang/resolve/kotlin/VirtualFileKotlinClassFinder.kt

@@ -16,9 +16,6 @@
 
 package org.jetbrains.jet.lang.resolve.kotlin
 
-import com.intellij.ide.highlighter.JavaClassFileType
-import com.intellij.openapi.vfs.VirtualFile
-import org.jetbrains.annotations.Nullable
 import org.jetbrains.jet.lang.resolve.java.structure.JavaClass
 import org.jetbrains.jet.lang.resolve.java.structure.impl.JavaClassImpl
 import org.jetbrains.jet.lang.resolve.name.FqName
@@ -38,10 +35,6 @@ public abstract class VirtualFileKotlinClassFinder() : VirtualFileFinder {
             file = file.getParent()!!.findChild(classFileName(javaClass) + ".class").sure("Virtual file not found for $javaClass")
         }
 
-        if (file.getFileType() != JavaClassFileType.INSTANCE) {
-            return null
-        }
-
         return KotlinBinaryClassCache.getKotlinBinaryClass(file)
     }