Fix printing wine version with custom WINELOADER

- Don't call bp::search_path when using WINELOADER. It will return an
  empty string for an absolute path.

- To match the behaviour of the exe wrapper scripts, only print the
  wine version from WINELOADER if the path is executable.

src/plugin/utils.cpp

@@ -16,6 +16,7 @@
 
 #include "utils.h"
 
+#include <unistd.h>
 #include <boost/dll/runtime_symbol_info.hpp>
 #include <boost/process/io.hpp>
 #include <boost/process/pipe.hpp>
@@ -343,16 +344,17 @@ std::vector<boost::filesystem::path> get_augmented_search_path() {
 std::string get_wine_version() {
     // The '*.exe' scripts generated by winegcc allow you to override the binary
     // used to run Wine, so will will respect this as well
-    std::string wine_command = "wine";
-
+    std::string wine_path;
     bp::environment env = boost::this_process::environment();
-    if (!env["WINELOADER"].empty()) {
-        wine_command = env["WINELOADER"].to_string();
+    const std::string wineloader_path = env["WINELOADER"].to_string();
+    if (access(wineloader_path.c_str(), X_OK) == 0) {
+        wine_path = wineloader_path;
+    } else {
+        wine_path = bp::search_path("wine");
     }
 
     bp::ipstream output;
     try {
-        const fs::path wine_path = bp::search_path(wine_command);
         bp::system(wine_path, "--version", bp::std_out = output);
     } catch (const std::system_error&) {
         return "<NOT FOUND>";