build/i18n-scan.pl: avoid a possible endless loop

Issuing './build/i18n-scan.pl libs/core/' leads to this
endless loop with some perl implementations:

<...>
Use of uninitialized value in concatenation (.) or string at../build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
Use of uninitialized value in concatenation (.) or string at ./build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
Use of uninitialized value in concatenation (.) or string at ./build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
Use of uninitialized value in concatenation (.) or string at ./build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
Use of uninitialized value in concatenation (.) or string at ./build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
Use of uninitialized value in concatenation (.) or string at ./build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
Use of uninitialized value in concatenation (.) or string at ./build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
Use of uninitialized value in concatenation (.) or string at ./build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
Use of uninitialized value in concatenation (.) or string at ./build/i18n-scan.pl line 69.
substr outside of string at ./build/i18n-scan.pl line 69.
<...>

Experienced with this perl version:
"This is perl, v5.8.8 built for i386-linux"

Fix it by undefining the 'sub' variable if it is an
empty string.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

diff --git a/build/i18n-scan.pl b/build/i18n-scan.pl
index 8807384..3f73271 100755 (executable)
--- a/build/i18n-scan.pl
+++ b/build/i18n-scan.pl
@@ -64,6 +64,10 @@ if( open F, "find @ARGV -type f '(' -name '*.htm' -o -name '*.lua' ')' |" )
                                        {
                                                ( $sub, $code ) = extract_delimited($code, q{'"}, q{\s*(?:\.\.\s*)?});
 
+                                               if( length($sub) < 1 ) {
+                                                       undef $sub;
+                                               }
+
                                                if( defined $sub )
                                                {
                                                        $res .= substr $sub, 1, length($sub) - 2;