fix the default fallback for suball()

src/tests/sub.vtc

@@ -75,6 +75,10 @@ varnish v1 -vcl {
 			= b.sub("b", req.http.undef, "rewrite undef");
 		set resp.http.undefrewritef
 			= re2.sub("b", "b", req.http.undef, "rewrite undef");
+
+		# Default fallbacks
+		set resp.http.fallback = b.sub("acd", "x");
+		set resp.http.fallbackf = re2.sub("b", "acd", "x");
 	}
 
 } -start
@@ -117,6 +121,9 @@ client c1 {
 
 	expect resp.http.undefrewrite == "rewrite undef"
 	expect resp.http.undefrewritef == "rewrite undef"
+
+	expect resp.http.fallback == "**SUB METHOD FAILED**"
+	expect resp.http.fallbackf == "**SUB FUNCTION FAILED**"
 } -run
 
 logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {

src/tests/suball.vtc

@@ -77,6 +77,10 @@ varnish v1 -vcl {
 			= b.suball("b", req.http.undef, "rewrite undef");
 		set resp.http.undefrewritef
 			= re2.suball("b", "b", req.http.undef, "rewrite undef");
+
+		# Default fallbacks
+		set resp.http.fallback = b.suball("acd", "x");
+		set resp.http.fallbackf = re2.suball("b", "acd", "x");
 	}
 } -start
 
@@ -118,6 +122,9 @@ client c1 {
 
 	expect resp.http.undefrewrite == "rewrite undef"
 	expect resp.http.undefrewritef == "rewrite undef"
+
+	expect resp.http.fallback == "**SUBALL METHOD FAILED**"
+	expect resp.http.fallbackf == "**SUBALL FUNCTION FAILED**"
 } -run
 
 logexpect l1 -v v1 -d 1 -g vxid -q "VCL_Error" {

src/vmod_re2.vcc

@@ -63,7 +63,7 @@ $Function STRING sub(STRING pattern, STRING text, STRING rewrite,
 		     BOOL perl_classes=0, BOOL word_boundary=0, BOOL one_line=0)
 
 $Function STRING suball(STRING pattern, STRING text, STRING rewrite,
-                        STRING fallback = "**SUB FUNCTION FAILED**",
+                        STRING fallback = "**SUBALL FUNCTION FAILED**",
 		        BOOL utf8=0, BOOL posix_syntax=0, BOOL longest_match=0,
 		        INT max_mem=8388608, BOOL literal=0, BOOL never_nl=0,
 		        BOOL dot_nl=0, BOOL never_capture=0,