Modify the descritions of seq_file and flowchart

7.4 The seq_file is missing the behavior that occurs when it
directly returns NULL after the start step.

Also, in the flowchart, the first decision where `return is NULL`
is `Yes` points to nothing, which is not defined in ISO 5807.

ISO 5807 section 10.3.1.2 states logic path of a decision,
"Each exit from a symbol be accompanied by the appropriate
condition values to show the logic path which it represents,
so that the conditions and the associated references are identified."

The behavior of pointing to nothing does not have associated
references and does not indicate the relation of this logic path.

Refs:
	1. The Liunx Kernel Module Programming Guide
	   7.4 Manage /proc file with seq_file
	2. ISO-5807-1985

lkmpg.tex

@@ -1234,7 +1234,7 @@ \subsection{Manage /proc file with seq\_file}
 The \cpp|seq_file| API starts a sequence when a user read the \verb|/proc| file.
 
 A sequence begins with the call of the function \cpp|start()|.
-If the return is a non \cpp|NULL| value, the function \cpp|next()| is called.
+If the return is a non \cpp|NULL| value, the function \cpp|next()| is called; otherwise, otherwise, the \cpp|stop()| function is called directly.
 This function is an iterator, the goal is to go through all the data.
 Each time \cpp|next()| is called, the function \cpp|show()| is also called.
 It writes data values in the buffer read by the user.
@@ -1251,13 +1251,12 @@ \subsection{Manage /proc file with seq\_file}
   \begin{tikzpicture}[node distance=2cm, thick]
     \node (start) [startstop] {start() treatment};
     \node (branch1) [decision, below of=start, yshift=-1cm] {return is NULL?};
-    \node (emptynode) [right of=branch1, xshift=2cm] {Yes};
     \node (next) [process, below of=branch1, yshift=-1cm] {next() treatment};
     \node (branch2) [decision, below of=next, yshift=-1cm] {return is NULL?};
     \node (stop) [startstop, below of=branch2, yshift=-1cm] {stop() treatment};
 
     \draw [->] (start) -- (branch1);
-    \draw [->] (branch1) -- node[anchor=east] {} (emptynode);
+    \draw [->] (branch1.east) to [out=135, in=-135, bend left=45] node [right] {Yes} (stop.east);
     \draw [->] (branch1) -- node[left=2em, anchor=south] {No} (next);
     \draw [->] (next) -- (branch2);
     \draw [->] (branch2.west) to [out=135, in=-135, bend left=45] node [left] {No} (next.west);