fix read_cmdline API and a small buglet where "[comm]" may be too narrow

function                                             old     new   delta
func_args                                             25      26      +1
read_cmdline                                         119     114      -5
display_process_list                                1462    1447     -15
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/2 up/down: 1/-20)             Total: -19 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/procps.c b/libbb/procps.c
index 9a8e42d..9746617 100644
--- a/libbb/procps.c
+++ b/libbb/procps.c
@@ -464,18 +464,19 @@
 
 void FAST_FUNC read_cmdline(char *buf, int col, unsigned pid, const char *comm)
 {
-	ssize_t sz;
+	int sz;
 	char filename[sizeof("/proc//cmdline") + sizeof(int)*3];
 
 	sprintf(filename, "/proc/%u/cmdline", pid);
-	sz = open_read_close(filename, buf, col);
+	sz = open_read_close(filename, buf, col - 1);
 	if (sz > 0) {
 		buf[sz] = '\0';
 		while (--sz >= 0 && buf[sz] == '\0')
 			continue;
-		while (--sz >= 0)
+		do {
 			if ((unsigned char)(buf[sz]) < ' ')
 				buf[sz] = ' ';
+		} while (--sz >= 0);
 	} else {
 		snprintf(buf, col, "[%s]", comm);
 	}