net-installer: fix fallback line

First of all, `IF ERRORLEVEL <n>` means: "if the last program  run
returned an exit code equal to *or greater than* the number specified"
(emphasis added). Therefore, `IF NOT ERRORLEVEL 0` has no chance of ever
succeeding.

Second, we cannot really rely on Bash being installed correctly, so
let's just ask the user to acknowledge the error messages by pressing a
key.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

net-installer/setup-git-sdk.bat

@@ -41,4 +41,4 @@
 @REM now clone the Git sources, build it, and start an interactive shell
 @bash --login -c "mkdir -p /usr/src && cd /usr/src && git clone -b @@GIT_BRANCH@@ -c core.autocrlf=false https://github.com/git-for-windows/git && cd git && make install; bash -i"
 
-@IF NOT ERRORLEVEL 0 bash --login -i
+@IF ERRORLEVEL 1 PAUSE