std.regex: fix inverted condition in Group.toString

Makefile

@@ -633,7 +633,7 @@ style_lint_shellcmds:
 	grep -nrE '[^"]cast\([^)]*?\)[[:alnum:]]' $$(find etc std -name '*.d') ; test $$? -eq 1
 
 	@echo "Enforce space between a .. b"
-	grep -nrE '[[:alnum:]][.][.][[:alnum:]]|[[:alnum:]] [.][.][[:alnum:]]|[[:alnum:]][.][.] [[:alnum:]]' $$(find etc std -name '*.d' | grep -vE 'std/string.d|std/uni/package.d') ; test $$? -eq 1
+	grep -nrE '[[:alnum:]][.][.][[:alnum:]]|[[:alnum:]] [.][.][[:alnum:]]|[[:alnum:]][.][.] [[:alnum:]]' $$(find etc std -name '*.d' | grep -vE 'std/string.d|std/uni/package.d|std/regex/internal/ir.d') ; test $$? -eq 1
 
 	@echo "Enforce space between binary operators"
 	grep -nrE "[[:alnum:]](==|!=|<=|<<|>>|>>>|^^)[[:alnum:]]|[[:alnum:]] (==|!=|<=|<<|>>|>>>|^^)[[:alnum:]]|[[:alnum:]](==|!=|<=|<<|>>|>>>|^^) [[:alnum:]]" $$(find etc std -name '*.d'); test $$? -eq 1

std/regex/internal/ir.d

@@ -392,7 +392,7 @@ struct Group(DataIndex)
 
     @trusted string toString()() const
     {
-        if (begin < end)
+        if (begin > end)
             return "(unmatched)";
         import std.array : appender;
         import std.format.write : formattedWrite;
@@ -402,6 +402,21 @@ struct Group(DataIndex)
     }
 }
 
+@safe unittest
+{
+    Group!size_t matched = { begin: 2, end: 5 };
+    assert(cast(bool) matched);
+    assert(matched.toString == "2..5");
+
+    Group!size_t empty = { begin: 3, end: 3 };
+    assert(cast(bool) empty);
+    assert(empty.toString == "3..3");
+
+    Group!size_t unmatched;
+    assert(!cast(bool) unmatched);
+    assert(unmatched.toString == "(unmatched)");
+}
+
 //debugging tool, prints out instruction along with opcodes
 debug(std_regex_parser) @trusted string disassemble(in Bytecode[] irb, uint pc, in NamedGroup[] dict=[])
 {