Fix: extLowBlock and extHighBlock must be relative to start of EBR

They cannot be assigned from rootLowBlock/rootHighBlock because these
are relative to start of disk. This was causing child partitions
in EBR to get de_LowCyl and de_HighCyl values which are relative to
start of disk, while these must be relative to start of EBR or writes
will happen "after end of disk". Problem visible when there are MBR
partitions covering at least half of disk before EBR partition.

Author: deadwood

workbench/c/Partition/main.c

@@ -121,7 +121,7 @@
 #define MAX_SFS_SIZE (124L * 1024)
 #define MAX_SIZE(A) (((A) == &sfs0) ? MAX_SFS_SIZE : MAX_FFS_SIZE)
 
-const TEXT version_string[] = "$VER: Partition 42.0 (18.05.2023)";
+const TEXT version_string[] = "$VER: Partition 42.1 (17.04.2025)";
 
 static const struct PartitionType fat32 = { "FAT\2", 4 };
 static const struct PartitionType dos3 = { "DOS\3", 4 };
@@ -161,8 +161,8 @@ int main(void)
     const struct PartitionType *sysType = NULL, *workType = NULL;
     LONG error = 0, sysSize = 0, workSize = 0, sysHighCyl, lowCyl, highCyl,
         reqHighCyl, unit, hasActive = FALSE;
-    QUAD rootLowBlock = 1, rootHighBlock = 0, extLowBlock = 1,
-        extHighBlock = 0, lowBlock, highBlock, rootBlocks, extBlocks;
+    QUAD rootLowBlock = 1, rootHighBlock = 0; /* Blocks relative to disk start */
+    QUAD lowBlock, highBlock, rootBlocks, extBlocks;
     ULONG scheme = PHPTT_MBR;
     UWORD partCount = 0;
 
@@ -428,8 +428,6 @@ int main(void)
                     }
                     if (extPartition && !activePart)
                         activePart = extPartition;
-                    extLowBlock = rootLowBlock;
-                    extHighBlock = rootHighBlock;
                     rootLowBlock = 1;
                     rootHighBlock = 0;
                     partCount++;
@@ -444,6 +442,8 @@ int main(void)
 
     if (error == 0)
     {
+        QUAD extLowBlock = 1,  extHighBlock = 0; /* Block relative to EBR start */
+
         /* Find largest gap in extended partition */
         if (extPartition != NULL)
         {