fix(RegionMap): distinguish clean EOF from partial read in load()

Previously load() returned true unconditionally on file-open success,
masking truncated or corrupt /regions2 files. Additionally, the first
field of each entry record (r->id) used the same success-chaining
pattern as subsequent fields, so a clean EOF at a record boundary set
success=false and would have been indistinguishable from real
corruption once the return value was fixed.

The r->id read is now split out: n==0 is a clean EOF (break, success
retains its prior value from the header read), n!=sizeof(r->id) is a
partial read or corruption (break, success=false). load() now returns
success instead of an unconditional true, so its return value reflects
the actual parse outcome.

Companion fix to #2372, which fixed the same return-true hardcoding
in save(). (#1891 originally reported this on load() but was closed
when #2372 landed — that PR only touched save(); this addresses the
load() side.)

src/helpers/RegionMap.cpp

@@ -93,13 +93,15 @@ bool RegionMap::load(FILESYSTEM* _fs, const char* path) {
         while (num_regions < MAX_REGION_ENTRIES) {
           auto r = &regions[num_regions];
 
-          success = file.read((uint8_t *) &r->id, sizeof(r->id)) == sizeof(r->id);
+          int n = file.read((uint8_t *) &r->id, sizeof(r->id));
+          if (n == 0) break;  // clean EOF
+          success = (n == sizeof(r->id));
           success = success && file.read((uint8_t *) &r->parent, sizeof(r->parent)) == sizeof(r->parent);
           success = success && file.read((uint8_t *) r->name, sizeof(r->name)) == sizeof(r->name);
           success = success && file.read((uint8_t *) &r->flags, sizeof(r->flags)) == sizeof(r->flags);
           success = success && file.read(pad, sizeof(pad)) == sizeof(pad);
 
-          if (!success) break; // EOF
+          if (!success) break;  // partial read or corruption
 
           if (r->id >= next_id) {    // make sure next_id is valid
             next_id = r->id + 1;
@@ -108,7 +110,7 @@ bool RegionMap::load(FILESYSTEM* _fs, const char* path) {
         }
       }
       file.close();
-      return true;
+      return success;
     }
   }
   return false;  // failed