chore: Warn about unused resulted values that really should be used

If the developer doesn't check whether FAT or NitroFS have been
initialized correctly, it won't be possible to show a sensible error
message to the user of the application when something fails later. It
is very important to verify that they have been initialized correctly
and to show a message to the user so that they know what happened.

include/fat.h

@@ -22,6 +22,7 @@ extern "C" {
 /// This function calls fatInit() with the default cache size (5 pages = 20 KB).
 ///
 /// @return It returns true on success, false on error.
+WARN_UNUSED_RESULT
 bool fatInitDefault(void);
 
 /// This function initializes the FAT filesystem with a default cache size.
@@ -53,6 +54,7 @@ bool fatInitDefault(void);
 ///
 /// @return
 ///     It returns true on success, false on error.
+WARN_UNUSED_RESULT
 bool fatInit(int32_t cache_size_pages, bool set_as_default_device);
 
 /// This function returns the default current working directory.

include/filesystem.h

@@ -30,6 +30,7 @@ extern "C" {
 ///
 /// @return
 ///     It returns true on success, false on error.
+WARN_UNUSED_RESULT
 bool nitroFSInit(const char *basepath);
 
 /// Exits NitroFS.

source/arm9/libc/nitrofs.c

@@ -640,20 +640,27 @@ bool nitroFSInit(const char *basepath)
     // Try to open the basepath file.
     if (basepath)
     {
-        fatInitDefault();
-        nitrofs_local.file = fopen(basepath, "r");
-
-        // Initialize the FAT lookup cache for NitroFS files.
-        // NitroFS files inherently do a lot of seeking, so it's almost always
-        // beneficial. At the same time, for a defragmented drive, this should
-        // only occupy a few dozen bytes.
-        //
-        // FIXME: Move this to the DLDI driver space and remove the 2KB
-        // size limit.
-        if (!nitrofs_local.file)
-            basepath = NULL;
+        if (fatInitDefault())
+        {
+            nitrofs_local.file = fopen(basepath, "r");
+
+            // Initialize the FAT lookup cache for NitroFS files.
+            //
+            // NitroFS files inherently do a lot of seeking, so it's almost
+            // always beneficial. At the same time, for a defragmented drive,
+            // this should only occupy a few dozen bytes.
+            //
+            // FIXME: Move this to the DLDI driver space and remove the 2KB
+            // size limit.
+            if (nitrofs_local.file == NULL)
+                basepath = NULL;
+            else
+                fatInitLookupCacheFile(nitrofs_local.file, 2048);
+        }
         else
-            fatInitLookupCacheFile(nitrofs_local.file, 2048);
+        {
+            basepath = NULL;
+        }
     }
 
     // Read FNT/FAT offset/size information.