Fix string max length check

Earle F. Philhower, III · Earle F. Philhower, III · commit c0a6b2779945 · 2019-01-28T15:26:22.000-08:00
We only have 15, not 16, bits of length, so adjust the check
accordingly.
diff --git a/cores/esp8266/WString.cpp b/cores/esp8266/WString.cpp
@@ -153,8 +153,8 @@ unsigned char String::reserve(unsigned int size) {
 }
 
 unsigned char String::changeBuffer(unsigned int maxStrLen) {
-    if (maxStrLen > 0xffff) {
-        // Sanity check len can fit in 16-bits
+    if (maxStrLen > 0x7fff) {
+        // Sanity check len can fit in 15-bits
         return 0;
     }
     // Can we use SSO here to avoid allocation?

Original file line number	Diff line number	Diff line change
`@@ -153,8 +153,8 @@ unsigned char String::reserve(unsigned int size) {`
`153`	`153`	`}`
`154`	`154`
`155`	`155`	`unsigned char String::changeBuffer(unsigned int maxStrLen) {`
`156`		`- if (maxStrLen > 0xffff) {`
`157`		`- // Sanity check len can fit in 16-bits`
	`156`	`+ if (maxStrLen > 0x7fff) {`
	`157`	`+ // Sanity check len can fit in 15-bits`
`158`	`158`	`return 0;`
`159`	`159`	`}`
`160`	`160`	`// Can we use SSO here to avoid allocation?`