Fix CA2022 warnings: avoid inexact Stream.Read calls

GVFS/GVFS.Common/Git/GitRepo.cs

@@ -153,7 +153,7 @@ private static bool ReadLooseObjectHeader(Stream input, out long size)
             size = 0;
 
             byte[] buffer = new byte[5];
-            input.Read(buffer, 0, buffer.Length);
+            input.ReadExactly(buffer, 0, buffer.Length);
             if (!Enumerable.SequenceEqual(buffer, LooseBlobHeader))
             {
                 return false;

GVFS/GVFS.Common/HealthCalculator/EnlistmentHydrationSummary.cs

@@ -196,7 +196,7 @@ internal static int GetIndexFileCount(GVFSEnlistment enlistment, PhysicalFileSys
                  * the 4 bytes at offsets 8-11 of the index file. */
                 indexFile.Position = 8;
                 var bytes = new byte[4];
-                indexFile.Read(
+                indexFile.ReadExactly(
                     bytes, // Destination buffer
                     offset: 0, // Offset in destination buffer, not in indexFile
                     count: 4);

GVFS/GVFS.UnitTests/Mock/ReusableMemoryStream.cs

@@ -67,7 +67,7 @@ public string ReadAt(long position, long length)
             this.Position = position;
 
             byte[] bytes = new byte[length];
-            this.Read(bytes, 0, (int)length);
+            this.ReadExactly(bytes, 0, (int)length);
 
             this.Position = lastPosition;
 

GVFS/GVFS.Virtualization/Projection/GitIndexProjection.GitIndexParser.cs

@@ -391,7 +391,11 @@ private FileSystemTaskResult ParseIndex(
 
             private void ReadNextPage()
             {
+                // Last page may be smaller than PageSize; partial fill is safe because
+                // the parser stops after entryCount entries and never reads stale bytes.
+#pragma warning disable CA2022 // Avoid inexact read
                 this.indexStream.Read(this.page, 0, PageSize);
+#pragma warning restore CA2022
                 this.nextByteIndex = 0;
             }