backend/ninja: fix off-by-one in cmd length estimate

This causes us to not count the spaces between arguments, thereby
undercounting the number of elements. This is extra important because we
previously double counted all actual characters, covering this issue up.

Fixes: cf0fecfce ("backend/ninja: Fix bug in NinjaRule.length_estimate")

mesonbuild/backend/ninjabackend.py

@@ -292,7 +292,7 @@ class NinjaRule:
         estimate = len(command)
         for m in re.finditer(r'(\${\w+}|\$\w+)?[^$]*', command):
             if m.start(1) != -1:
-                estimate -= m.end(1) - m.start(1) + 1
+                estimate -= m.end(1) - m.start(1)
                 chunk = m.group(1)
                 if chunk[1] == '{':
                     chunk = chunk[2:-1]