patch 8.2.0957: compiler warning for uninitialized variable

Problem:    Compiler warning for uninitialized variable. (Tony Mechelynck)
Solution:   Initialize one variable.
diff --git a/src/spell.c b/src/spell.c
index 8558d39..b3d9b0a 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -207,7 +207,7 @@
     if (spell_iswordp(mi.mi_fend, wp))
     {
 	int prev_upper;
-	int this_upper;
+	int this_upper = FALSE;  // init for gcc
 
 	if (use_camel_case)
 	{