Fix 7-zip solid archive detection

src/SharpCompress/Archives/SevenZip/SevenZipArchive.cs

@@ -194,7 +194,10 @@ protected override IReader CreateReaderForSolidExtraction() =>
         new SevenZipReader(ReaderOptions, this);
 
     public override bool IsSolid =>
-        Entries.Where(x => !x.IsDirectory).GroupBy(x => x.FilePart.Folder).Count() > 1;
+        Entries
+            .Where(x => !x.IsDirectory)
+            .GroupBy(x => x.FilePart.Folder)
+            .Any(folder => folder.Count() > 1);
 
     public override long TotalSize =>
         _database?._packSizes.Aggregate(0L, (total, packSize) => total + packSize) ?? 0;

tests/SharpCompress.Test/SevenZip/SevenZipArchiveTests.cs

@@ -204,4 +204,23 @@ public void SevenZipArchive_Tar_PathRead()
             Path.Combine(TEST_ARCHIVES_PATH, "7Zip.Tar.tar")
         );
     }
+
+    [Fact]
+    public void SevenZipArchive_TestSolidDetection()
+    {
+        using var oneBlockSolidArchive = SevenZipArchive.Open(
+            Path.Combine(TEST_ARCHIVES_PATH, "7Zip.solid.1block.7z")
+        );
+        Assert.True(oneBlockSolidArchive.IsSolid);
+
+        using var solidArchive = SevenZipArchive.Open(
+            Path.Combine(TEST_ARCHIVES_PATH, "7Zip.solid.7z")
+        );
+        Assert.True(solidArchive.IsSolid);
+
+        using var nonSolidArchive = SevenZipArchive.Open(
+            Path.Combine(TEST_ARCHIVES_PATH, "7Zip.nonsolid.7z")
+        );
+        Assert.False(nonSolidArchive.IsSolid);
+    }
 }