Fix LibraryLoader crash on error during context-transfer restoration

- Track whether transferred thread's original context was successfully restored.
- In the catch block, leak the remote allocation instead of freeing it if the thread was not restored; this prevents the target process from executing freed memory.
- Remove redundant 'op == 0x55' check in InstructionAnalyzer (already matched by (op & 0xF8) == 0x50).
- Simplify MemoryBase ReadString align-down expression to previousLen - (previousLen % nullLen).
- Change StubAllocator size parameter from nint to int for clarity (internal test seam).

Tests: 199 passing, 4 integration/interactive skipped.

WhiteMagic/Injection/DllInjector.cs

@@ -209,6 +209,8 @@ public sealed class DllInjector
                 throw new InvalidOperationException($"SuspendThread failed (error {error}).");
             }
 
+            bool restored = false;
+
             try
             {
                 IntPtr result;
@@ -257,6 +259,8 @@ public sealed class DllInjector
                         int error = Marshal.GetLastPInvokeError();
                         throw new InvalidOperationException($"ResumeThread restore failed (error {error}).");
                     }
+
+                    restored = true;
                 }
                 else
                 {
@@ -302,6 +306,8 @@ public sealed class DllInjector
                         int error = Marshal.GetLastPInvokeError();
                         throw new InvalidOperationException($"ResumeThread restore failed (error {error}).");
                     }
+
+                    restored = true;
                 }
 
                 if (result == IntPtr.Zero)
@@ -311,8 +317,15 @@ public sealed class DllInjector
             }
             catch
             {
-                // Best effort: resume the thread if we left it suspended.
-                _ = NativeMethods.ResumeThread(thread);
+                // If we never successfully restored the thread's original context, the
+                // thread may still be executing (or about to execute) code inside the
+                // injected allocation. Freeing that memory now would crash the target
+                // process, so leak the block and leave the thread suspended.
+                if (!restored)
+                {
+                    remoteBase = IntPtr.Zero;
+                }
+
                 throw;
             }
         }