Trim reversed stacks to prevent sort check from failing

If the last line of the stack starts with a space, then the space is used in sorting.
However, the space is removed when the line is then fed into the flamegraph, which
makes the sorting invalid. This commit adds a trim to the reverse process to fix this.

src/flamegraph/mod.rs

@@ -429,6 +429,7 @@ where
             }
             stack.push(' ');
             stack.push_str(&line[samples_idx..]);
+            let stack = stack.trim();
             reversed.push(&stack);
         }
         let mut reversed: Vec<&str> = reversed.iter().collect();

tests/data/flamegraph/fractional-samples/with-space.txt

@@ -0,0 +1,6 @@
+cksum;_start;__libc_start_main;main;cksum 31.23
+cksum;cksum 6.1
+cksum;cksum;__GI___fread_unlocked;_IO_file_xsgetn;_IO_file_read;entry_SYSCALL_64_fastpath_[k];sys_read_[k];vfs_read_[k];__vfs_read_[k];ext4_file_read_iter_[k] 1.4
+cksum;main;core::array::<impl core::default::Default for [T; _]>::default::h67c9877e6f2a615c 19.0
+noploop;[unknown] 2.567
+noploop;main 274.321

tests/flamegraph.rs

@@ -806,6 +806,18 @@ fn flamegraph_reversed_stack_ordering_with_fractional_samples() {
     test_flamegraph(input_file, expected_result_file, options).unwrap();
 }
 
+#[test]
+fn flamegraph_reversed_stack_ordering_with_space() {
+    let input_file = "./tests/data/flamegraph/fractional-samples/with-space.txt";
+    let expected_result_file = "./tests/data/flamegraph/fractional-samples/with-space-reversed.svg";
+
+    let mut options = flamegraph::Options::default();
+    options.hash = true;
+    options.reverse_stack_order = true;
+
+    test_flamegraph(input_file, expected_result_file, options).unwrap();
+}
+
 #[test]
 fn flamegraph_should_warn_about_no_sort_when_reversing_stack_ordering() {
     let mut options = flamegraph::Options::default();