Fix off-by-one string indexing in constraint checking

Also change string comparison type to `StringComparison.Ordinal`, which
should be the correct type according to
https://docs.microsoft.com/en-us/dotnet/standard/base-types/best-practices-strings.

Author: al2me6

ModuleManager/Extensions/StringExtensions.cs

@@ -30,7 +30,7 @@ public static bool Contains(this string str, string value, out int index)
             if (str == null) throw new ArgumentNullException(nameof(str));
             if (value == null) throw new ArgumentNullException(nameof(value));
 
-            index = str.IndexOf(value, StringComparison.CurrentCultureIgnoreCase);
+            index = str.IndexOf(value, StringComparison.Ordinal);
             return index != -1;
         }
     }

ModuleManager/MMPatchLoader.cs

@@ -1548,7 +1548,7 @@ public static bool CheckConstraints(ConfigNode node, string constraints)
                 string remainingConstraints = "";
                 if (constraints.Contains(":HAS[", out int hasStart))
                 {
-                    hasStart += 4;
+                    hasStart += 5;
                     remainingConstraints = constraints.Substring(hasStart, constraintList[0].LastIndexOf(']') - hasStart);
                     constraints = constraints.Substring(0, hasStart - 5);
                 }