build-openssl.bat: Added check for OpenSSL source directory

projects/build-openssl.bat

@@ -104,6 +104,9 @@ rem ***************************************************************************
 
   rem Check we have Visual Studio installed
   if not exist "%PF%\%VC_PATH%" goto novc
+
+  rem Check the start directory exists
+  if not exist "%START_DIR%" goto noopenssl
 
 :configure
   if "%BUILD_PLATFORM%" == "" (
@@ -282,7 +285,7 @@ rem ***************************************************************************
   echo.
   echo Other:
   echo.
-  echo directory - Specifies the openssl directory
+  echo directory - Specifies the OpenSSL source directory
   goto error
 
 :unknown
@@ -305,11 +308,16 @@ rem ***************************************************************************
   echo Error: %VC_DESC% is not installed
   goto error
 
-:nox64
-  echo.
-  echo Error: %VC_DESC% does not support 64-bit builds
-  goto error
-
+:nox64
+  echo.
+  echo Error: %VC_DESC% does not support 64-bit builds
+  goto error
+
+:noopenssl
+  echo.
+  echo Error: Cannot locate OpenSSL source directory
+  goto error
+
 :error
   if "%OS%" == "Windows_NT" endlocal
   exit /B 1