Fix heap corruption caused by specifying an x value outside of display

Bug:
The memory corruption occurs during the memset call in the erase
routine.  When bad values are in drawBitmap the number of bytes to zero
is too long by 1 byte.  These values are updated by several macros, one
of which is pageCheckBoundsRange.  The values passed to this macro
should be x values that match physical pixels on the screen.  However
calls to drawBitmap was using the number of screen pixels or width to
offset the current x value resulting in the next pixel (not updated)
instead of the last pixel (updated).  When the bitmap or a portion of
the bitmap is at the edge of the screen, this results in an invalid x
value outside the range of (0 <= x < width).

Fix:
* Compute the last updated pixel offset for the pageCheckBoundsRange in
drawBitmap
* Add comments to pageCheckBounds* macros to specify bounds in hopes of
avoiding a similar issue in the future

Author: LeeLeahy2

src/qwiic_grssd1306.cpp

@@ -130,6 +130,8 @@
     } while (false)
 
 // Macro to check and adjust record bounds based on a single location
+// The _x_ value must be within the screen (0 <= x < width), limit
+// values are ignored
 #define pageCheckBounds(_page_, _x_)                                                                                   \
     do                                                                                                                 \
     {                                                                                                                  \
@@ -140,6 +142,8 @@
     } while (false)
 
 // Macro to check and adjust record bounds using another page descriptor
+// The _page2_ x values must be within the screen (0 <= x < width), limit
+// values are ignored
 #define pageCheckBoundsDesc(_page_, _page2_)                                                                           \
     do                                                                                                                 \
     {                                                                                                                  \
@@ -150,6 +154,7 @@
     } while (false)
 
 // Macro to check and adjust record bounds using bounds values
+// Values _x0_ and _x1_ must be within the screen (0 <= x < width)
 #define pageCheckBoundsRange(_page_, _x0_, _x1_)                                                                       \
     do                                                                                                                 \
     {                                                                                                                  \
@@ -880,7 +885,7 @@ void QwGrSSD1306::drawBitmap(uint8_t x0, uint8_t y0, uint8_t dst_width, uint8_t
         bmp_y += neededBits;
 
         pageCheckBoundsRange(m_pageState[iPage], x0,
-                             x0 + dst_width); // mark dirty range in page desc
+                             x0 + dst_width - 1); // mark dirty range in page desc
     }
 }
 
@@ -1014,4 +1019,4 @@ void QwGrSSD1306::sendDevCommand(uint8_t command, uint8_t value)
 void QwGrSSD1306::sendDevData(uint8_t *pData, uint8_t nData)
 {
     m_i2cBus->writeRegisterRegion(m_i2cAddress, kDeviceSendData, pData, nData);
-}
+}