Define an image limit in a place where it is easy to adjust if needed.

src/BlueSCSI_cdrom.cpp

@@ -843,7 +843,7 @@ void cdromReinsertFirstImage(image_config_t &img)
     {
         // Multiple images for this drive, force restart from first one
         debuglog("---- Restarting from first CD-ROM image");
-        img.image_index = 9;
+        img.image_index = IMAGE_INDEX_MAX;
         cdromSwitchNextImage(img);
     }
     else if (img.ejected)

src/BlueSCSI_disk.cpp

@@ -535,7 +535,7 @@ int scsiDiskGetNextImageName(image_config_t &img, char *buf, size_t buflen)
     int target_idx = img.scsiId & 7;
 
     img.image_index++;
-    if (img.image_index > 9)
+    if (img.image_index > IMAGE_INDEX_MAX)
     {
         img.image_index = 0;
     }

src/BlueSCSI_disk.h

@@ -39,6 +39,8 @@ extern "C" {
 #include <scsi.h>
 }
 
+#define IMAGE_INDEX_MAX 9
+
 // Extended configuration stored alongside the normal SCSI2SD target information
 struct image_config_t: public S2S_TargetCfg
 {
@@ -62,7 +64,7 @@ struct image_config_t: public S2S_TargetCfg
     uint32_t tape_pos;
 
     // Index of image, for when image on-the-fly switching is used for CD drives
-    int image_index;
+    uint8_t image_index = IMAGE_INDEX_MAX;
 
     // Cue sheet file for CD-ROM images
     FsFile cuesheetfile;