Don't report unsupported file types as 'corrupted' captures

* This adds a specific error message if even the magic number doesn't look like
  a supported file type.

renderdoc/api/replay/renderdoc_tostr.inl

@@ -63,6 +63,7 @@ rdcstr DoStringise(const ResultCode &el)
         FileIncompatibleVersion,
         "Capture file incompatible due to being made on an different major version of RenderDoc");
     STRINGISE_ENUM_CLASS_NAMED(FileCorrupted, "File is corrupted");
+    STRINGISE_ENUM_CLASS_NAMED(FileUnrecognised, "File format is unrecognised");
     STRINGISE_ENUM_CLASS_NAMED(
         ImageUnsupported, "The image file or format is unrecognised or not supported in this form");
     STRINGISE_ENUM_CLASS_NAMED(APIUnsupported, "API used in this capture is unsupported");

renderdoc/api/replay/replay_enums.h

@@ -3803,6 +3803,10 @@ a remote server.
 
   The capture file is corrupted or otherwise unrecognisable.
 
+.. data:: FileUnrecognised
+
+  The file was not recognised as any supported file type.
+
 .. data:: ImageUnsupported
 
   The image file or format is unrecognised or not supported in this form.
@@ -3895,6 +3899,7 @@ enum class ResultCode : uint32_t
   FileIOFailed,
   FileIncompatibleVersion,
   FileCorrupted,
+  FileUnrecognised,
   ImageUnsupported,
   APIUnsupported,
   APIInitFailed,

renderdoc/serialise/rdcfile.cpp

@@ -329,9 +329,8 @@ void RDCFile::Init(StreamReader &reader)
 
   if(header.magic != MAGIC_HEADER)
   {
-    SET_ERROR_RESULT(m_Error, ResultCode::FileCorrupted,
-                     "Invalid capture file. Expected magic %08x, got %08x.", MAGIC_HEADER,
-                     (uint32_t)header.magic);
+    SET_ERROR_RESULT(m_Error, ResultCode::FileUnrecognised,
+                     "Unrecognised file type. File magic number is %08x.", (uint32_t)header.magic);
     return;
   }