tryfix abspath c func with "" on windows

Author: IanButterworth

src/init.c

@@ -575,6 +575,14 @@ static char *abspath(const char *in, int nprefix)
         }
     }
 #else
+    // GetFullPathName intentionally errors if given an empty string so manually insert `.`
+    if (strlen(in) - nprefix == 0) {
+        size_t path_size = JL_PATH_MAX;
+        char *in2 = (char*)malloc_s(JL_PATH_MAX);
+        memcpy(in2, in, nprefix);
+        in2[nprefix+1] = '.';
+        in = in2;
+    }
     DWORD n = GetFullPathName(in + nprefix, 0, NULL, NULL);
     if (n <= 0) {
         jl_error("fatal error: jl_options.image_file path too long or GetFullPathName failed");