fixes:

- typo fix in comment
- At least on some Win10 machines, attempting to execute a *non-existent* `"%NASMPATH%\nasm.exe"` will cause the subsequent `%ERRORLEVEL% equ 0` check to **pass** inadvertently, hence we MUST first check whether the indicated nasm.exe exists, truly, before running this version test/check in the installer batch script.
- At least on Win10, when NASM had already been previously installed using the standard Windows NASM installer application, the path to the nasm.exe WILL contain spaces (`C:/Program Files...`) and we must make sure our installer batch script correctly deals with this scenario, requiring paths to be surrounded by `"` double quotes.
- Expanded the error/progress messages in the installer batch script a bit to make them more useful and legible when the `NASMPATH` environment variable has not been set up or is (probably erroneously) *empty*: now at least one of the installer progress messages allows the user to diagnose this scenario.

Author: GerHobbelt

README.md

@@ -1,5 +1,6 @@
 VSNASM
 =============
+
 [![Github All Releases](https://img.shields.io/github/downloads/ShiftMediaProject/VSNASM/total.svg)](https://github.com/ShiftMediaProject/VSNASM/releases)
 [![GitHub release](https://img.shields.io/github/release/ShiftMediaProject/VSNASM.svg)](https://github.com/ShiftMediaProject/VSNASM/releases/latest)
 [![GitHub issues](https://img.shields.io/github/issues/ShiftMediaProject/VSNASM.svg)](https://github.com/ShiftMediaProject/VSNASM/issues)

install_script.bat

@@ -309,18 +309,20 @@ if %ERRORLEVEL% neq 0 (
     echo    Ensure that this script is run in a shell with the necessary write privileges
     goto Terminate
 )
-REM Check if nasm is alredy found before trying to download it
+REM Check if nasm is already found before trying to download it
 echo Checking for existing NASM in NASMPATH...
-%NASMPATH%\nasm.exe -v >nul 2>&1
-if %ERRORLEVEL% equ 0 (
-    echo Using existing NASM binary from %NASMPATH%...
-    goto SkipInstallNASM
-) else (
-    echo ..existing NASM not found in NASMPATH.
+if exist "%NASMPATH%\nasm.exe" (
+    "%NASMPATH%\nasm.exe" -v >nul 2>&1
+    if %ERRORLEVEL% equ 0 (
+        echo "Using existing NASM binary from %NASMPATH%\nasm.exe..."
+        goto SkipInstallNASM
+    ) else (
+        echo "..existing NASM not found in NASMPATH=%NASMPATH%."
+    )
 )
 REM Download the latest nasm binary for windows
 if exist "%SCRIPTDIR%\nasm_%NASMVERSION%.zip" (
-    echo Using existing NASM archive...
+    echo Using existing NASM installer archive...
     goto InstallNASM
 )
 set NASMDOWNLOAD=%NASMDL%/%NASMVERSION%/win%SYSARCH%/nasm-%NASMVERSION%-win%SYSARCH%.zip