Fix bug where column is specified for own line

When the syntax `expected-error@:42{{}}` was used, this would
accidentally trigger "absolute line" mode, despite not specifying a
line, resulting in the target line always being line 0.

Author: hnrklssn

lib/Frontend/DiagnosticVerifier.cpp

@@ -700,7 +700,7 @@ unsigned DiagnosticVerifier::parseExpectedDiagInfo(
       Offs = MatchStart.slice(2, TextStartIdx).rtrim();
     else {
       Offs = MatchStart.slice(1, TextStartIdx).rtrim();
-      if (Offs[0] != '-')
+      if (Offs[0] >= '0' && Offs[0] <= '9')
         AbsoluteLine = true;
     }