Fix error message

This fixes the error message

  error: file `' was not found in the Nix search path (add it using $NIX_PATH or -I)

1 files changed, 4 insertions, 3 deletions

diff --git a/src/libexpr/common-opts.cc b/src/libexpr/common-opts.cc
index e0865d9fcc..0ee889a995 100644
--- a/src/libexpr/common-opts.cc
+++ b/src/libexpr/common-opts.cc
@@ -47,9 +47,10 @@ bool parseSearchPathArg(const string & arg, Strings::iterator & i,
 Path lookupFileArg(EvalState & state, string s)
 {
     if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
-        Path p = state.findFile(s.substr(1, s.size() - 2));
-        if (p == "") throw Error(format("file `%1%' was not found in the Nix search path (add it using $NIX_PATH or -I)") % p);
-        return p;
+        Path p = s.substr(1, s.size() - 2);
+        Path p2 = state.findFile(p);
+        if (p2 == "") throw Error(format("file `%1%' was not found in the Nix search path (add it using $NIX_PATH or -I)") % p);
+        return p2;
     } else
         return absPath(s);
 }