Terminate the output directory argument of flatc.

Given the command

flatc -o . -c test.fbs

it would generate header file

.test_generated.h

rather than

./test_generated.h

This fixes this issue.

Tested:
Manually verified that flatc generates the correct output files given output
paths ending with and without '/' on Linux and Windows.

Bug: 16464827
Change-Id: I854cb881286f22690f1885f942cf3fd2fc59ca8d

src/flatc.cpp

@@ -134,6 +134,10 @@ int main(int argc, const char *argv[]) {
         case 'o':
           if (++i >= argc) Error("missing path following", arg, true);
           output_path = argv[i];
+          if (!(output_path.back() == flatbuffers::kPathSeparator ||
+                output_path.back() == flatbuffers::kPosixPathSeparator)) {
+            output_path += flatbuffers::kPathSeparator;
+          }
           break;
         case 'S':
           opts.strict_json = true;
@@ -212,4 +216,3 @@ int main(int argc, const char *argv[]) {
 
   return 0;
 }
-