Increase the size of the last hole if the new hole aligns to it

Author: rafalmiel

src/hole.rs

@@ -240,11 +240,15 @@ fn deallocate(mut hole: &mut Hole, addr: usize, mut size: usize) {
                 hole.size += size + next.size; // merge the F and Y blocks to this X block
                 hole.next = hole.next_unwrap().next.take(); // remove the Y block
             }
-            Some(_) if hole_addr + hole.size == addr => {
+            _ if hole_addr + hole.size == addr => {
                 // block is right behind this hole but there is used memory after it
                 // before:  ___XXX______YYYYY____    where X is this hole and Y the next hole
                 // after:   ___XXXFFFF__YYYYY____    where F is the freed block
 
+                // or: block is right behind this hole and this is the last hole
+                // before:  ___XXX_______________    where X is this hole and Y the next hole
+                // after:   ___XXXFFFF___________    where F is the freed block
+
                 hole.size += size; // merge the F block to this X block
             }
             Some(next) if addr + size == next.addr => {