Fix branching commands.

If a label isnt specified, jump to end of script, not the last command
in the script.

Print an error and exit if you try and jump to a non-existant label

Works for the following testcase
# cat strings
a
b
c
d
e
f
g
# cat strings | ./busybox sed -n '/d/b;p'
a
b
c
e
f
g

1 files changed, 18 insertions, 13 deletions

diff --git a/editors/sed.c b/editors/sed.c
index 7174288a2..aa3ce024e 100644
--- a/editors/sed.c
+++ b/editors/sed.c
@@ -475,9 +475,11 @@ static char *parse_cmd_str(sed_cmd_t * sed_cmd, char *cmdstr)
                 int length;
 
                 cmdstr += strspn(cmdstr, " ");
-                length = strcspn(cmdstr, "; \n");
-                sed_cmd->label = strndup(cmdstr, length);
-                cmdstr += length;
+                length = strcspn(cmdstr, semicolon_whitespace);
+                if (length) {
+                        sed_cmd->label = strndup(cmdstr, length);
+                        cmdstr += length;
+                }
         }
         /* translation command */
         else if (sed_cmd->cmd == 'y') {
@@ -771,13 +773,11 @@ static sed_cmd_t *branch_to(const char *label)
         sed_cmd_t *sed_cmd;
 
         for (sed_cmd = sed_cmd_head.next; sed_cmd; sed_cmd = sed_cmd->next) {
-                if ((sed_cmd->label) && (strcmp(sed_cmd->label, label) == 0)) {
-                        break;
+                if ((sed_cmd->cmd == ':') && (sed_cmd->label) && (strcmp(sed_cmd->label, label) == 0)) {
+                        return (sed_cmd);
                 }
         }
-
-        /* If no match returns last command */
-        return (sed_cmd);
+        bb_error_msg_and_die("Can't find label for jump to `%s'", label);
 }
 
 static void process_file(FILE * file)
@@ -998,12 +998,17 @@ static void process_file(FILE * file)
                                                 linenum++;
                                         }
                                         break;
-                                case 'b':
-                                        sed_cmd = branch_to(sed_cmd->label);
-                                        break;
                                 case 't':
-                                        if (substituted) {
-                                                sed_cmd = branch_to(sed_cmd->label);
+                                        if (substituted)
+                                                /* Fall through */
+                                case 'b':
+                                        {
+                                                if (sed_cmd->label == NULL) {
+                                                        /* Jump to end of script */
+                                                        deleted = 1;
+                                                } else {
+                                                        sed_cmd = branch_to(sed_cmd->label);
+                                                }
                                         }
                                         break;
                                 case 'y':{