Fixed exception on opening non-Kotlin class file.

#EA-35266 fixed

idea/src/org/jetbrains/jet/plugin/libraries/JetClsFileDecompiledPsiFileProvider.java

@@ -31,6 +31,10 @@ public class JetClsFileDecompiledPsiFileProvider implements ClsFileDecompiledPsi
     @Nullable
     @Override
     public PsiFile getDecompiledPsiFile(@NotNull PsiJavaFile psiFile) {
-        return JetDecompiledData.getDecompiledData((ClsFileImpl) psiFile).getJetFile();
+        ClsFileImpl clsFile = (ClsFileImpl)psiFile;
+        if (JetDecompiledData.isKotlinFile(clsFile)) {
+            return JetDecompiledData.getDecompiledData(clsFile).getJetFile();
+        }
+        return null;
     }
 }

idea/src/org/jetbrains/jet/plugin/libraries/JetDecompiledData.java

@@ -80,9 +80,10 @@ public class JetDecompiledData {
 
     public static boolean isKotlinFile(@NotNull Project project, @NotNull VirtualFile vFile) {
         ClsFileImpl clsFile = getClsFile(project, vFile);
-        if (clsFile == null) {
-            return false;
-        }
+        return clsFile != null && isKotlinFile(clsFile);
+    }
+
+    public static boolean isKotlinFile(@NotNull ClsFileImpl clsFile) {
         PsiClass psiClass = clsFile.getClasses()[0];
         return DecompiledDataFactory.isKotlinNamespaceClass(psiClass) || DecompiledDataFactory.isKotlinClass(psiClass);
     }